Yata

And He is the only example (if I don't remember wrong) of both Stormlight and Shardplate Enhanced in the modern time

I have no proofs but I suppose that an Allomancer fueled by Breath would work exactly like a Mist fueled Allomancer. After all you simply change where your Spiritual pipe take energy (yeah Spiritual Pipe is an horrible name, I know) without change the mechanics of Allomancy. But of course I may be wrong But indeed it's a fascinating question.

Actually we know it.

But the fact that the metal doesn't contain power, doesn't mean that Metal isn't Scadrial's Focus. It's like to say that Nalthis's focus isn't Command because the Command Itself isn't power but you take the Investiture from Breath to performe magic. The Metals are Scadrial's Focus. You may see it quite perfectly from the Scadrial's Cognitive Realm where every source of Metal brights both if it an Metallic Arts viable metals and not. The reason Ruin and Preservation are MetalBlind, it because to their expanded senses, the metal glow to much to read whaterver information they keep.

Yeah the Idea is quite baseless but it's possible and indeed interesting. There is only a single thing that bother me about this idea, Threnody is classificated as "minor Shardworld" aka a World without a significative Shardic Influence. I really doubt a place so relevant are lefted without control Brandon said (I think near December) he want to work again on Threnody, therefore maybe we may get new informations.

The Stormlight as Honor's Investiture is a speculation, we have no evidence about. And instead it's more likely to be of Cultivation or other Source at all (for example I think it's Adonalsium Investiture lefted before the Shattering). Returning to the main topic as far as I know there isn't any WoB who said that Scadrial's Focus isn't Metal but just one who say: "The Metals aren't invested themself but they are gateway to power"

A cognitive Shadow is quite a ghost of someone (and usually it's a pretty rare condition). You can't have a Cognitive Shadow if the subject isn't dead. I say that because it seems you aren't to familiar with the concept. It may exist a Tanavast(Honor)'s Cognitive Shadow because He is dead, but Cultivation and Odium are pretty alive. Therefore no Cognitive Shadows for them.

This is false, we see Medallion with 2 power all the times. For example while Allik is on the airship he has a Medallion with Feruchemical iron and F Connection. Simply He has not a Medallion with Feruchemical iron, fheat and F-Connection at the same time and he can't change Medallions all the time while they are in air to avoid too weight change. The Medallion (with F-Iron and F-Durallumin) itself are described to be made of three parts: A Nicrosil Unsealed one contains the powers, an Iron one to store the the weight and a Duralluminium one to tap Connection for. Allik himself said he saw a Medallion with three powers a couple of time in his life.

Probably I am wrong about the possibility of an old Mistborn to burn Trellium (unless "trell" was on Scadrial from a lot of time but I find it unlikely), but I think the quoted part is not so sure. The Medallion tech we saw seems to point elsewhere. A nircosilmind may be filled with many abilities at once. We saw them all the time in the book. It's never stated there are more pieces of Nicrosil in a Medallion (the coin is a perfect example) Hemalurgy doesn't allow to steal multiple attributes with a single Spike but this don't say anything about how the Soulbearer's power works.

of course, here the link About the BoM you have right. Shardblades are more invested than the BoM but also the Shardplade are probably less Invested than Shardblade and Half-Shard too. But those items are capable of stopping a Shardblade. Another thing to considerate is that a replice of the Spearhead made only of a single metal (to keep the previous example Tin) full of Feruchemical tin would be as Invested as the BoM. It wil not be a godlike weapon but for the Investiture-density point of view they are the same thing

@Argel I rememeber the WoB about Hoid and Hemalurgy, but if I remember right, Hoid doesn't have Spikes because He will not let to open himself to external influences (through Hemalurgy's weakness)

Will we ever see different Magic Systems spawned by the same Shards in different Shardworlds (because the Shard moved) ?

Yes I know the theory about the "other-material-spikes" but to be honest I always find it quite no-sense. It's like to remove the focus from the magic system. The Hemalurgy's focus (or to be more precise The Scadrial's Focus) is Metal and so long that Ruin (Harmony) is Invested in Scadrial and the Hemalurgy exist, you are bind to its rules. You can't performe Hemalurgy without. But it's not this topic's matter therefore sorry for the digression

As far as I know there isn't any canon direct information about Trellium=Godmetal. But as soon as you think about it can't be something else. The Trellium is a metal who is compatible with the Metallic Arts and it's a metal outside of Harmony's portfollio. The Metallic Arts works only with the 16 right metal (8 base metals + 8 of Base Metals's alloys) and with godmetals (that in my mind are quite a little hack to the metallic arts) and their alloys. It's stated by someone with the full understanding of the Realmatic Theory and the quite godlike Knowledge therefore I immagine we may take this words as true. Therefore if Sazed said that it's not a mundane metal. This mean it have to be a supernatural metal born from another entity (this mean Shards or their offspring).

I don't think it's true. The Shards as far as we see don't create solid embodiments of their power.. the only natural outcome of Shard's power are the Shardpool. The Atium exist only because a Shard (preservation) made a willing act to condensate the stolen part of Ruin in the Pits of Hatsin in solid form (power that I think Sazed didn't retrived from there). The Lerasium in the same way was (probably) created by Leras as a Willing Act, not for some nature factor (I have a theory about the remaining beads of Lerasium were used in the past but it's beyond this topic's point)

Yeah it was my idea too (also if I place as Adonalsium Spren also Stormfather and Nightwatcher).

The "fatique" effect after his show made me think that he try (maybe with success) to bond with all the near Humans to feed of them in some way (maybe to try to restore his former mind).

No man, Leras (Preservation) made possible Seer and Malatium's Misting to made possible to have an army who may burn Ruin's body. But it's a messing of a Shard in the magic who fuels. The Mist were setted to made this possible thousand of years ago. The MistSnapping was a tool to create more Allomancer than before and to made possible the Seer's birth. It's was designed to Snap a precise fraction of the popolation to suggest a Intelligent Guide. We have not sure proof but Sazed fixed this because there is no more need of this trick when he changed the Snapping method. EDIT: From Coppermind

It's impossible to be a Godmetal misting in nature. Leras have to made trick and messing with the Snapping to get his own Seer Army. This mean that unless Sazed create this specific Misting, nobody other than a Mistborn may burn trellium. I always try to avoid the "godlike direct action" in those kind of problem, because everything became leterally a Deus Ex Machina and as you said quite surelly Harmony already know every effect of the Trellium (I use the "quite" only because the stealth propriety of Trellium may be an issue to Harmony's knowledge) I agree with Rasarr about the possible Trellium's Allomantic Effect. The stealth path is the right one to me. I though about Invisibility physical and Cognitive but I may be wrong. About the balance of the godmetal's power, to me it's meaningless. It's possible that a Godmetal may be quite useless in a Metallic Art without ruin (ok bad joke) nothing. It's not an rpg where the power need to be on the same tier.

Like @Argent said we appretiate Cosmere's Knowledge in every form. Your question are very interesting, some time ago we start a topic about the Savantism and we struck about the possibility to steal the Savant improved abilities. Now we have an official information. I am really surprised abou the Coppercloud & Life Sense....I have to re-think better to this Breath's ability.

I see it differently. If a Mistborn stored his Spirit-Web (and there are a 95% that this happen because we know there was a Mistborn in the BoM's Research team). The BoM will contain the whole spectrum of Mistborn's power... As "I can burn everything". this to me means that a BoM's user may burn the 16 metals, Atium and its alloys, Lerasium (but actually everybody may do this), Harmonium, Trellium, Raysium,ecc.. It's the reason I doubt the Bands may be used to access to Feruchemical Trellium, unless a Full Feruchemist take part to the project.

Nightblood is made by 1000 Breath not 10000. It's still an high number but for example a Divine Breath is more Invested

Like Voidus said, without a Mistborn we can't know it and there is the same problem with the Feruchemical effect without a Full Feruchemist. But to be Honest the Kandra may discover the Allomantic Trellium effect, in the BoM there are the full array of Allomantic Power, while I am unsure if a Full Feruchemist take part to its creation.

Maybe there isn't a real pattern... Just the Radiant (probably an Elsecaller or WillShaper) with the mission to lock the Oathgate, failed his mission for an unknown reason (enemy or simply He/she don't get there in time and the Oathbreak began to affect him/her). I think they lock the Gates from the Cognitive and some issues may happen in the dangerous realm of the Spren (much more while you are killing a lot of them)