The Sovereign

I think we can look to Sunlit Man for a suitable explanation;

It does make sense for Reason to be attracted to the Math Planet.

I've been thinking about this more; I suspect Rayse set up the Duralumin around his Perpendicularity to hide it from Honor and Cultivation. When the Honor-Odium clash shattered the plains some gaps were made in the Duralumin which allowed the Chasmfiends and later the Listeners to hear the Tones coming from it and find it.

I could see that too. Both seems plausible to me.

It's directly referenced, but not named in Mistborn: Secret History as well and is canonically named in some of the Ars Arcanums.

I'll go into broader thoughts on the book when I have more time but a few quick notes: -Stormseat was sitting on top of a huge pile of Duralumin? "Not Aluminum but something greater". -Axendweth was likely the "Terriswoman Nurse" who "took care" of Lemex. -Does Shallan have a 5th Sibling or is one of her Siblings a half sibling? (Likely Helaran)

There is a comment about Dai-Gonarthis just wanting to destroy, I would guess her cost is to be let off the leash so to speak. Aimia's scouring was likely a cost of her's.

Answers to my predictions:

-Shallan's final truth will be "I caused all this to start again when I killed my mother, Chanarach. She went back to Braize and broke." -Thude will be revealed to have already bonded a Lightspren and used his Stoneshaping to help the Listener Elderly/Children escape Narak. The Chasmsfiends are docile because of his Stoneshaping. -The missing Dustbringers are grouped under Chanarach similarly to the Skybreakers under Nale. -Auxiliary is Szeth's Highspren, -There is a Dawnshard on the Shattered Plains, The Chasmsfiends pupate there because they help guard it. -The above mentioned Dawnshard is what Shattered the Plains. -El's metal Carapace are Hemalurgic Spikes. -Adolin will Swear the first and second ideals of the Edgedancers specifically related to Listening to and caring for the Deadeyes, this will finally fully revive Maya. -Shallan is Pregnant. -Szeth will die. -Kaladin will Ascend to Honor. -Gavinor will have a Spiritual Realm connection experience with Elohkar.

I suspect that we will find a collection of Dustbringers grouped under Chanarach. An extremely speculative theory I have is that Chana was planning on doing something similar to what Nale was doing pre-Everstorm and ended up trying to Kill Shallan not because she bonded a Spren, but because she bonded the wrong type of Spren.

There are a couple things to consider; First and most importantly, Shallan is not a reliable narrator. Whatever specifically happened the night her mother died beyond Shallan killing her with Testament, Lin taking the blame for it, and possibly that her mother tried to kill her it isn't exactly what Shallan has said/alluded to. Second, regarding why Nale wouldn't get directly involved; I suspect this has to do with the theory that Shallan's mother is Chanarach. If this was indeed the case (which seems very likely to me), that could be why Nale didn't involve himself directly.

Thude was the first new age Willshaper and had fulfilled the 2nd Oath when he help the Elderly and Young Listeners escape Narak. He protected them in the Chasms during the clash of the Highstorm & Everstorm with Stoneshaping.

You've convinced me. I agree, this is likely just shown out of order.

The musings on the first day don't have to be specifically referring to him have control over the humans that he gained in this Interlude. Presumably El knows the details of the Conflict of Champions and what the contract says. Working with the assumption that the Odium will win, then he knows as a Fused who is sane (even stripped of his Title and Rhythms) he would be placed above the vast majority of Odium's post victory forces.

Did anyone else get Thrawn vibes from El?

I think this is more like when Kelsier looked into Preservation's eyes/Dalinar looked into Odium's eyes; Kal may have been getting a small glimpse into the Spiritual Realm.

He doesn't? He has a backwards shadow. We have seen this several times before, it's just the Cognitive representation of someone who's Spirit Web has been altered by Investiture. Lift can see it because she sees partially into the Cognitive Realm. We can narrow this down somewhat; He hadn't reclaimed it when Szeth was made Truthless and banished and he had it in Tukar so we have a roughly 8 year window.

I suspect it has to do with the Nature of what Inkspren are:

Picking nits is fun sometimes... Wind And Truth: Chapter 14, Section 2:

I don't think we actually have enough information to "know" this. It is possible one of them have a Enlightened Cryptic but it could be an Enlightened Mistspren; We know Renarin's Illumination surge is wonky but what is to say that is true of all Enlightened Mistspren? It is possible some have normal Illumination and Wonky Progression instead. Also if it is true that Lieke doesn't have a Spren, then either Iyatil or Mraize has a Enlightened Inkspren or Lightspren since one of them has access to the surge of Transportation. Another very interesting tidbit from these chapters: Spren don't have to manifest, even in Shadesmar. But, it is something that needs to be learned.

Another couple of potential reasons that Shallan didn't see the Spren: 1.) Like Glys, the Enlightened Spren can actually go inside the body of its Bonded Radiant. 2.) The Spren is an Enlightened Inkspren and made itself extremely small as we've seen with Ivory. I'm not sure if Inkspren can change their size in Shadesmar, but I believe we also do not know that they cannot.

All Radiants have some Connection to the Cognitive Realm due to the Nahel Bond itself; Lightweavers have a more of a Connection due to their Transformation Surge, Willshapers have an even stronger Connection because of their Transportation Surge, Elscallers have the strongest Connection because of their access to both Transformation and Transportation. Shallan essentially has a double Connection via double access to Transformation (think of Vin's Bronze Allomancy when she was Spiked), I suspect it is about equal to the Connection of a Willshaper. While I fully agree with the Shallan is Chanarach's Daughter theory, I do not think that is involved in what is happening here outside of potentially making her a more appealing candidate for a Spren to bond with in the first place.

I'm sure there is more to it, but bringing others is likely the first major difference.