Incredible theory, just read through the topic and I had a blast, congratulations OP and everyone who participated. There are many ifs, but I have few doubts that Chana is Shalan's mother, or "creator" I guess, or least I like to believe it
I'm not sure about the relationship of Shalan's mother death and the desolations, though it would make sense for it to be connected, as it makes so much sense in her progression to admit to have caused something that catastrophic, but then again it does seem like the scheme was long going before her.
Here's my take:
She admits to being responsable for the last desolation, thinks it's her 5th, but it doesn't work (failed oath Kaladin style in OB makes a great story beat), the story progresses, until she eventually admits the hardest of truths:
It wasn't actually her fault, none of it
I think this would work in the logic of progression that oaths seem to have, besides, while a bit corny, I find it to be a very sweet character arc.
And it would explain why, while you can be lead to believe they were connected, logic dictated the last desolation was being planned way before her time.
I agree with many that the glowing thing that was put back into the safe is important and not just an hallucination, and honestly it doesn't make much sense to me for Shalan's father to put the blade in the safe, why would that be the reaction?
Besides, if Shallan is a terrified child, wouldn't she dismiss the blade immediatly? (I might be forgetting something here)
I really like this. I can totally see an herald being so terrified of accidentally dying that they carry around a failsafe, a gemstone to trap their soul rather than going back to be tortured.
It's not unlikely to think that the Ghostbloods had some trick up their sleeve to bring her back from the gemstone she gets trapped in. The father would be instructed, in case it happend, to immediatly put the gemstone to safety.
Finally, 2 cents on Taln, but this is pure speculation cause I think it'd be cool: He was driven to madness and kept in Braize voluntarily waiting for the right moment fora long time, and released when he was supposed to, cause he still has a part to play in Odium's plan.