I agree with the theory of Odium/Taravangian trying to force a tie.
I take your points of Odium choosing someone who is linked to another planet, and I see it as posible, but also dificult to accomplish (first Odium can't leave Rosharan System, second he will have to find someone loyal to him with no honor/cultivation/odium influence to make the shadesmar interplanetary trip, third the traveller has to convince the choosen champion to accept by giving him/her something he/she wants, and finally all of this will have to be settled in ten days or less). But as I said, It's a possibility.
I don't agree with those who are saying the campion will be a child, because a child technically can kill Dalinar, so he will have to concede his defeat to escape from killing the child or the child will have to concede his defeat. My perception is that if a champions can technically be killed by the other, a tie is not an option. So, on both situations, Taravangian will lose (remember his goal is to broke the ties which stop him to escape from rosharan system).
Odium's champion being an spren/voidspren it's another possibility. We assume sprens/voidsprens can't interact with physic world (despite Syl doing it) but what if high ranked sprens can do it? Lately has been demonstrated that spren knowledge is not absolute, and their nature is likely to be changed (for example, Maya as a deadeyes can speak). On the other side, navani has demonstrated that sprens and voidsprens can be killed with anti-stormlight and anti-voidlight. My conclusion is that common sprens can't be elected as champions, neither common voidsprens.
My guess would be on Odium representing himself, he can't be killed by Dalinar as far as Taravangian knows, neither he can kill Dalinar (because of his pact with Honor). Yes, Taravangian could be killed by Dalinar if he uses Nightblood, but we don't know when Nightblood will be operative to absorb energy (remember that killing Rayse has put it in a kind of sleeping state) and he knows that nobody a part of him knows that Nightblood can be used to kill gods (neither vasher knows as far as we know, but I think he wouldn't be surprised if he ever finds it out). Anti-Voidlight won't be an option, Rebaniel itself constated that there was no possibility to create the amount of anti-voidlight needed to kill Odium.
I don't know if there is another entity likely to match with the restrictions to be the champion Odium needs. Cultivation is not an option, because she can kill Dalinar (she is not restrained by Odium's and Honor's pact). I think Hoid isn't option either, cause he will kill Dalinar to prevent Odium's escape. Perhaps Unmades or bondsmith's sprens like The Sibling or Nightwatcher can't be killed by the same reason as Odium.
If I'm wrong in a statement I made, please correct me. And I apologise in advance for my grammar mistakes. ;)