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Im not sure his madness left that much coherence. Ash certainly seems to have enough of the guilt and self-hate going on (see her destruction of her own images), and Nale has both acknowledged his own degradation and (very dryly) joked about Jezrien's madness so he might be self-aware enough for that sentiment.

I was thinking the Stormfather, which is why I thought it might require literal divine intervention. But the Fused do show that Cognitive shadows and spren can behave in very similar ways and are both entities of pure investiture, so a shadow/spren merger that doesnt require Shardic power does seem plausible.

Yes, at least Cognitive Shadows that can bring their own Physical form to the table, since being the anchor in the Physical Realm is one of their functions. At least one Herald has pulled it off, and they are cognitive shadows. For what it's worth, it's also apparently possible for a Cognitive Shadow to Merge with a spren. That might take shardic intervention, though.

For all those reasons with a more impressive physical capability and surprising utility: Horse

I've long assumed that the Lightning effect we've seen with Stormform is based on the Surge of Division since Lightning is fundamentally all about Charge separation. Whether is is possible with the "Decay" form of division available to Radiant, or whether any Order has any other distinct Division abilities, remains to be seen. Thematically speaking, Lightning as an advanced form of Fire Magic is not uncommon. Usually it only looses out to a more direct Air and/or Water=Weather Magic setup, in my experience.

It's no more OP that an elscaller soulcasting a person into flame, to me. As far as the actual effect (called Decay), there's apparently some discretion in how it manifests, presumably by the Intent of the user. It can be used to decay, burn, turn to dust, or other forms of decay and breakdown. That means a chunk of wood could become a pile of goo, sawdust, or flames depending on how the Dustbringer chooses to Release the stored chemical energy in the molecular Bonds.

Also as a datapoint: rather than just being the storage medium for the investiture. But Seons/Skaze should be able to provide that part of the Intent equation, and as you say it's entirely possible that a properly manipulated Dor could gain sapience just like

I dont think so, otherwise any shard piece of godmetal including plate would have that sort of innate realmic trait. [Mistborn]

I like it. You'd want to include some realmic Aons to let it cut Spiritually the way a Shardblade does, on top of extreme durability Investment. Mimicking the transport Summoning would likely be trickier, and might require a pre-programmed Storage location. [Stormlight Spoilers]

She (and most of the originals that have weighed in on the subject, including Hoid and Frost) seem to want Odium (and ruin for that matter) to have a custodian rather than risk it gaining sentience on it's own. Which is probably what Ambition is out there doing, since Rayse would have needed a reason to modify his M.O. after Ambition and before D&D.

And we have three characters that are confirmed to have been visited by Cultivation and not the Nightwatcher: Taravangian, Dalinar, and Lift. The first has ascended fully, and the second appears to have at least partially ascended That Time. The third asked that she stay the same and not become someone else and was given some weird Connection to Lifelight (and thus Cultivation) as part of it.

Short list of known effects: Chromium acts just like aluminum inside the body, causing any Allomancers touched by a Leecher to lose their metal reserves.[1] When burning away a person's metals, it feels like pulling power from the metal and returning it to an external source.[2] This power is similar to Nightblood and larkin.[3] When burning away a person's metals, non-Invested metals go before the Invested ones.[4] Only Allomantically relevant metals can be burned away.[5] The ability to burn the metal can be drained while leaving the metal.[2] A Leecher can also drain other forms of Investiture. They would be fairly effective at draining a person's Breath or Stormlight.[6] They could also Leech a Feruchemist who was tapping their metalmind.[7] They would be able to Leech from a Lifeless.[8] A Leecher could prevent a Shardbearer from summoning their blade,[9] and can prevent a weapon using Investiture from working.[2] If a Leecher touched Nightblood, they would die.[10] Metallic arts in opposition tip toward the stronger effect, and that appears to hold true instances where the form of Investiture doesnt give some specific situational advantage. Leeching feels like pulling power away and returning it to an external source, which implies to me that it gets channeled through the person like any other allomancy, leaving them open to Savantism dangers when used with Flairing, Duralumin, etc. All that to say they seem capable of the same general type of things as a Larkin and the Investiture-feeding part of Nightblood (but not his destroying in 3 realms side). Larkin will drain a fabrial but will not destroy the Spren, and since a Leecher only prevents a Shardbearer from summoning a blade rather than anything more permanent, I think a Leecher could not destroy a Spren/seon/cognitive shadow, though they might be able to destroy a spren's physical realm body (like a shardblade, Plate, or manifested fabrial). Leeching does not destroy Connections that we've seen. Given those two things I dont think they'd be able to actually destroy a Returned outright, but they could probably deplete the Returned's reserves and short-cut them to the end of the week feeding, which without a ready source (like a storm or maybe Mist) would amount to the same thing with extra steps. For a nicely Vague confirmation of the existence of limits:

I think she Had a stated goal and Endgame, she simply accomplished it by arranging the murder of Rayse, thus avenging her mate. I think her next Goal is going to be to arrange a successor so that she can let herself Retire. TOdium will probably prefer dealing with a young and inexperienced Shard so I expect he'll want to lay low until after the transition of power. My money's currently on Lift.

I think we may, but with the drive being a little more social. Bloodlines with the innate powers (or combinations of powers) vs those that don't have that genetic advantage and require Medallion tech (or spikes for the less scrupulous) to access and manipulate investiture.

The definitions can be suprisingly varried and personal in practice, but the main deciding factor is what is used to create it more than what it's final form is like. So anything non-animal that was soulcast would be Vegan by that definition. But just like the debates on whether lab-grown meat is Kosher (which from a quick google seem ongoing) likel it would likely be a matter of interpretation. Chouta is basically just a wrap, gyro, or burrito depending on how you imagine the flatbread part, but the filling can be anything. Soulcast meat is common in the camps, but it would qualify with or without meat (or meat-like) ingredients.

So the Stormfather at least is probably safe, and he's the one with the most (apparent) role in the broader rosharan Ecosystem. The Sibling could like follow the physical tower if it became a space-ship, though I dont knwo what the Light implications of that might be. Or even if the godspren (that arent bonded with divine ghosts) have any direct effect on the Lights of Roshar rather than just being heavily affected by them.

Might not be as big of a problem in Era 4 depending on how the current conflicts turn out, since there are two storms now...

Now, the implications of removing one of the three Godspren from Roshar would be a whole other issue. The Nightwatcher might not serve an ecological role on roshar itself, for example, but the Stormfather does.

You are definitely on to something. We know rosharans have somewhat less developed immune systems because of the Investiture rich ecosystem, which is why the world-hopper introduced Cold was such a strange thing to them. In the Space Age they could probably take steps to supplement it artificially (some smallish amount of Breath should do it) or ambient use fabrials similar RL sun-lamps in arctic areas, and actual Radiant's probably would have other issues but not being Under-Invested. Having a Bondsmith around to open Perpendicularities on the regular would also be helpful.

There will be some similar things with the RPG and Feruchemy, where it filled in details of the use and function of some (mostly spiritual) metals for the sake of game/setting completeness.

Off-hand: Chronicle Life could be an interesting being reminiscent of all kinds of passive Overserver cosmic beings of comic books fame. Anything that is about recording or observation, especially if it had a non-intervention mindset to the Command, could probably fall out that way. But even Destroy Evil could probably give you something way more laconic than Nightblood if you were imagining more of a Silent Juggernaut when you issued the "Destroy Evil" command. The Words are the main trigger, but the mental image behind them is where the real subtly of Awakening lives. Nightblood is definitely growing and evolving, though it's a slow process. I personally think that time he was asserting that Szeth was being Cruel is an indication that he's developing his own sense of morality. The strange thing for me has always been that he does have an innate measure of Evil in the way he "tests" others to provoke one of two reactions. This makes me think the issue is that Shashara only had a vague and emotional Sense of what she'd consider Evil, a "you know it when you see/feel it" mentality. She probably would have struggled to put it into articulate words and so Nightblood doesnt have a logical/cognitive Understanding of Evil but nevertheless he can identify a more Spiritual wavelength (a Rhythm, even?) that he uses to classify people, one that I think he got from the Internal Image side of the Command she used to create him. Awakening is governed by a lot more than the literal words, after all.

Vivenna's sword is more reticient than Nightblood, at the very least. It might have to do with having as "active" a Command as Destroy Evil that makes him outgoing, he wants to get to know people to see if they will give him an opportunity to Destroy what should be Destroyed (Called "Evil", but that's not a concept he actually gets).

Last I recall it was intended to be part of the eventual WoR Leatherbound Kickstarter, just like Dawnshard was for the Way of Kings one. Given how well Kickstarter has been working for them lately, I think that's likely to remain the plan.

The answer has evolved. Originally a mistborn would have needed a connection to the other shard/magic to be able to burn a foreign god-metal.

I may be mistaken but I believe the Push/Pull effect works natively on any mundane metal (other than aluminum), and has been shown to work on non-metals when boosted to high enough power levels. That's entirely separate from what can and cannot be burned, which is a topic that has seen some retcon recently. Best I can tell: Only the 16 mundane metals can be burned, and without shardic intervention only those 16 will have Mistings or Ferrings appearing in the S-Genome. Silver is not active in any of the Metallic arts, despite having some magical use in the cosmere overall. Godmetals are special; anyone can theoretically burn both scadrian ones, but Atium alloys require Mistborn or (unnatural) Mistings and all the Atium we've seen was actually an atium-electrum alloy which is why it couldn't be burned by anyone. In both (all?) cases their power seems to be accessed and/or manipulated via Alloying the metal with other things (mundane metals, other godmetals, etc) so mathematically there are a lot of possibilities that could be worthwhile. Agreed, to a Misting, the Alloy, etc is just a impure version of their main metal. There's been some retcon on metal poisoning: originally it was a thing in the books and in WOB but since about 2020 he's been saying they have an evolutionary resistance to it.