Nitpicking

Short of the immortal scholar Khriss, Sigzil is probably one of the most literate (and language-capable) people in the Cosmere. All Selish arts involve mastering a set of symbols. Also, he's very aligned with Devotion. I can absolutely see him becoming an Elantrian.

As mentioned upthread, Investiture leaks out of things. What "consumes" it is existence, in this model. I actually said in the threadstarter, if a person lived forever they could heal from becoming Drab, and that my proposed mystical practices to expand the tiny personal Perpendicularity could speed up the process. Healing Shardblade wounds would, of course, take even more Investiture but in principle be possible. It would be the Surge of Progression (or gold feruchemy) but slower.

Drifting, but Glys is probably even more complicated. We don't know the origin of Sja-Anat (who enlightened Glys). If, as I suspect, she was originally of Adonalsium, who knows what Shard her Investiture was assigned to at the Shattering. For all we know, Englightened spren have Whimsy's Investiture at some deep level.

So, Cosmere theorizing. In my head, that means arcanist stuff, not plot guessing (but that's a very valid topic). First round: I propose that there is an entire type of magic Brandon hasn't revealed yet. See, humans have Investiture. All sapients do, because the soul is Investiture. We know that losing some of that Investiture can slow healing, make one depressed and vulnerable to disease, etc. So, I speculate that all humans (and all living things, and maybe even all things) have a Connection to the Spiritual Realm and are always drawing a very small flow of Investiture into the Physical, which gets used to maintain their existence and then returns to the Spiritual. I further assert that somewhere in the Cosmere, people have developed mystical meditations and exercises that expand their tiny personal Perpendicularities, allowing them to work what we'd call "magic" without Connecting to a Cognitive entity (like a Shardbearer or Yoki-Hijo) or Spiritual entity (like an allomancer). In fact, I speculate further that we've seen such people ... if we've read Dragonsteel Prime. This implies that, say, a Drab could heal from their soul wound if they knew these techniques and lived long enough. It wouldn't occur to Endowment to spread that knowledge. She's all about gifting, not self-improvement. I speculate far too much when I say that if these people become savants, they become less and less material, superficially similar to the way we've seen a Soulcasting savant turn into air but not actually the same.

So now we need to ask Brandon: "What would happen if Sigzil/Nomad/Zellion tried to consume Nightblood as Nightblood tried to drain Sig's Investiture?" Nightblood is the most powerful Invested object in the Cosmere, at least in the Stormlight Archive period, but Sigzil's power comes from a Dawnshard. Followup question would be, "What if this happened while Sigzil was still the Dawnshard, not a sort of Sliver?" EDIT: We see Nomad Connect to Canticle shortly after arriving there. So ... he Skips to Sel. Connects to Arelon. And now he can draw on the nearly infinite, or at least unlimited, power of the Dor. And unthinkingly draws it all. And becomes the dishard of Leadership (Devotion + Dominion). I literally said "Holy sh!t" out loud when I thought of that.

You don't have to spoiler-warn the Stormlight Archive in this area.

SPOILER for White Sand

So that's what happened to Frost!

As I remember it, the Oathgate spren were getting ready to leave, seeing their role as over with the final disappearance of Odium and Honor.

On the other hand, the aluminum throne room did block the Connection between Maya and Adolin. Not sever it, but prevent them from using it.

So, it just occurred to me a few days ago that "Endowment" is a pretty straightforward synonym of "Providence". Both mean "giving something." I continue to think that Devotion and Dominion are taken from Zoroastrian beliefs (two of the Amesha Spenta), just as "Yasna" is a Persian/Farsi word meaning "prayer" (and pretty darn ironic in Brandon's usage). Any others?

They don't. Why do you assume T. is overthrown or destroyed? SPOILERS for the greater Cosmere:

I don't have Wind and Truth with me here, but didn't Retribution say he was going to inhale all the spren? Would that not include the Voidspren? The Voidspren were saved from being incorporated into Retribution as nothing but a source of Investiture by the Heralds and the Wind. And potentially, partly by the human and Singer freeing of Ba-Ado-Mishram. How will that affect their attitude in the Back Five?

We know that Enlightened Radiants (like Venli) can use Voidlight for the Surges. I expect they can also use Warlight.

I'm trying to avoid spoiling by implication, so I'll spoiler-hide the title: