Why Him? He's a terrific composer that earn's the loyalty of just about every director he works with. Tony Gilroy, M. Night Shyamalan and Christopher Nolan have all worked with him more than once, as have several others. The reason for that is his versatility and willingness to have a little fun - both desirable traits in a Star Wars score.
His score for Duplicity is great, and I listen to it about once every week or two. (The movie is also criminally underrated and overlooked, but that's another article.) The reason I mention Duplicity is not because it has any relation to what Episode VII will look or sound like, but as an example of how he can match the score to fit the vibe and feeling of the movie. It's a fun movie, that has fun with itself, and the music compliments this idea beautifully. On the flipside, his score for Blood Diamond, released the same year is gritty, brooding and intense. Plus,you have Batman Begins and The Dark Knight, which he co-wrote with Hans Zimmer (more from him in a minute). Those films couldn't be more opposite from Duplicity, and the scores keep up without missing a beat (pun intended). Next to John Williams, he's one of the most versatile composers working today.
He's also another composer who's jumped into established franchises before - The Bourne Legacy the most recent example of this.