I can't think of anything I want less than a Ziggler heel run. He is babyface material, it'd be a waste of one of the few big pops we see on WWE.
Yeah, it might not be a good time to turn him heel right now, anyways... Even though there are a shitload of heels, guys like Sheamus desperately need a turn, Sheamus needs it more. Plus, Rollins has that top heel spot and he's been doing a pretty good job.