Fraction definitely had it in him to do a very good Doom Patrol run, but the time for that has passed; he seems done with Big 2 stuff, and if he does do something at DC, it will be something that allows the requisite publicity and lets him say something important to him (I think he'd do a very nice Wonder Woman, for instance).
For me, the number one choice is without a doubt Mieville, though. If you've read his Dial H, you know that he channeled the creativity and erudition of Morrison's dP effortlessly, without in any way aping it.
Oh! Almost forgot John Rozum; his work on Xombi had a very similar vibe to Morrison's dP as well. He's never been much of a character writer, though.