I think The Banshee Queen would do a great job (if garrosh dies).
Hahaha, that will be really fun, like:
Thrall: Now... that the tirant is dead.... we need a new WARCHIEF!
*The horde army cheers*
Thrall: But... i...., i have made many mistakes... so i can't take these titles...
Thrall: We need to start from the begging... we need to leave the past of CORRUPTION and WAR behind US!
Thrall: We need someone... who have going throught many difficulties
*Cairne looks at Vol'jin*
Thrall: Someone how have been betrayed.... that have been in the doors of death
*Vol'jin though the scar in his neck*
Thrall: STAND TALL AND WELCOME YOUR NEW WARCHIEF!..... SYLVANAS WINDRUNNER!
I've stopped speculating. We'll either get some sort of strong hint in Shadows of the Horde or Blizz is going to hold it out on a stick until the last minute of the Siege. They're probably getting quite a kick out of us going back and forth about it this past year(I'm counting from the time of the announcement in the press release last year)
I think it's Voljin or Baines turn to be in the spotlight.
Thrall has kind of been written out of the story it seems, he's got a family and the whole earthen ring thing to deal with. Sylvannas and Lor'themar had their 5 minutes of fame already. Voljin and baine were just kind of hanging out twiddling their thumbs until this whole rebellion thing. I would have to assume one of them takes charge after.
My god I hope not. Thrall's day is done. If they do that, they're invalidating everything they've established (Thrall not wanting to be Warchief and wanting a family) over the past two expansions. I'm not saying I enjoyed the lore of Cataclysm, but I have enjoyed the lore of MoP. Both of them are no less important to the story.
If they did that, instead of taking the Horde somewhere new, I'd just...ugh.