I think as a wrestler, he'll be far better off as a face. He's not much at being the heel and controlling the pace of the match, due to his lack of...most things, like power, mat wrestling ability, good strikes, ring generalship, etc. If he can just sell sell sell then hit some of his Miz neckbreakers and the Breakdown, he'll probably look better in the ring.
As a character, I can kind of see it, but I think he might have too much "douche" and not enough "cool" in the equation. He'd be like Jericho or The Rock, but to me both of those guys are far more natural and a lot "cooler" than Miz. Miz tends to sound like a PR
spin machine when he speaks, and bragging about being the Most Must See WWE Superstar Sports Entertainer in the WWE Universe is inherently heelish.