We know that there is at least a chance and a prophecy of Parshendi bonding "human" spren. We also know that to bond a Voidspren, they must go into a highstorm. I suspect that in order to get a Parshendi Radiant, they will have to take a non void spren into an Everstorm. Ideas?
This is exactly what the chapter 34 epigram suggests when it states "destroys all lands he beholds, with spite". Also chapter 22, "it's coming brings the gods their night" (describing the Everstorm).
There is another vision (I forget who it is) where they discuss someone holding a child and the world begging him to slit its throat. I see these two together indicating that Odium will attempt to put a Radiant in the position of killing a child and turning their back on Honor or allowing the child to live, somehow dooming the world.
Isnt this pretty much what happened on Sel? We know that there were two shards, but multiple magic systems (soulstamps, AonDor, whatever the monks do, and ChayShan).
I think the Tranquiline Halls is actually Ashyn, the third world in the Greater Roshar system. This would make more sense, as this keeps all the activity in the same system.
DISCLAIMER: I have not read or heard any of the scenes from The Silence Divine.
My offbeat thought: there is someone out there already haging a number of followers and a claim of kingship. He also has support from the radiants. What about Highline Lopen?