It's not going to be Lor'themar, because the reaction would be, to quite one of Tolkien's friends who he read LotR to: "By god, not another bloody elf!". I know we all love Lor'themar because he's sensible and decent and so on, but I think we're about done with fancy wine-drinking elves, especially ones with fancy goatees, leading the SAVAGE HORDE.
Baine is totally viable. Not sure why everyone is so certain it won't be Thrall, and would be interested to hear the reasoning on that.