Re. Keita, yeah he did refuse to play there, but I don't think that's a good or bad thing. We all like to see players who give their all no matter what, but if he was shit as a LB and he knew he would hurt the team, it's better that he's honest. You're right, he's not very versatile.
My idea is indeed to sign a versatile midfielder to replace Toure. Initial thought was Raul Meireles, who was pretty good at the World Cup. But he's 27 and I'm not sure he'd want to be a backup. Plus no idea whether he's genuinely good defensively. And with Chygrinksiy gone, we do need cover at CB hence a more "backward oriented" midfielder. It's less risky playing kids in CM/AM than playing kids at CB.