Ok, I'm not as knowledgeable about all the theory as some of you are, but I'm confused as to why Eshonai isn't in the discussion. It seems like she is the obvious choice (which understandably makes me skeptical). She's a voidbringer, who has plate and blade. The fact that Odium's champion has plate and blade mean they've gotten it from somewhere. One of the existing KR would have to kill their spren to become the champion, and Dalinar is ruled out as a result, since the Stormfather won't become shards for him. I don't see Shallan or Kaladin killing their spren at this point, particularly not Kaladin, not after WoR. Shallan could go down that route, but I, like several of you, read her as healing more and more over time, and becoming stronger and more resilient as a result--as an aside, I genuinely wonder what her last truth will be.
So, to me, Eshonai makes the most sense. A voidbringer with plate and blade, one who has been utterly consumed by odium, despite the tiny inner voice protesting the change.