Kaladin could maybe fall in love with Shallan through her lying to him. If Shallan were to continue making bad decisions, I could see her pulling Kaladin down with her. She lies, and he believes her for some reason. Then Dalinar becomes aware of Shallan's descent into evil, and he kills her, making Kaladin, who has already become slowly compromised by his love for Shallan, shift into pure hatred for lighteyes. He then starts by killing Dalinar and becoming Odium's champion. Around the same time or prior to that, Szeth could cause a terrible accident that he has no way to blame on others, thus causing him to finally take his oathstone for himself. He could then be who he wants to be and become Honor's champion.
It's not completely thought out, but it's another possibility.
Also, first post!