I think Lor'themar could have been a good warchief, but he himself would be miserable and hate the position. He's always been a Farstrider at his heart.

Vol'jin would be a fool (something he's demonstratively not so far) to ignore Lor'themar's capabilities, so I hope he comes to utilize him instead of just sending him back to Quel'Thalas to hang out until the Horde needs help again. And as for Sylvanas...I sincerely hope she's not a future raid boss, thought at this point I can't see what else Blizzard is leading up to.