I think of the known youngish designers today, Posen, Tisci and maybe Theyskens are the ones who fit the enfant terrible / incroyable mode of Galliano and McQueen, that's right dammit that's what I said! I think that Posen has considerable raw talent, but at the same time can benefit from the discipline that comes from having suits there to tame his excessive tendencies.
Furthermore I think that what Posen has that fits into the current paradigm is charisma and people skills, because I don't care what anyone says, being able to say that you dressed Beyonce, Cate Blanchett, Kate Winslet and heck even Kim Kardashian carries a lot of weight with many of the potential big money customers from the U.S., Russia, Asia, and the Middle East. I don't know yet if I buy into the idea of Posen succeeding Galliano, I can wrap my head around Posen at Givenchy more than Dior, but it is not an entirely crazy idea.