You could always turn him back to the fair.Not a fan of the corporate Punk idea, tbh, it just somewhat kills of a huge part of his intricate and developing character/gimmick throughout his time in the WWE. Punk is known as the biggest anti-establishment guy on the roster, and, while it may produce quite a bit of heat, I think it would just be nonsensical and may hurt Punk in the long run.
I'd just have him return as a face, and issue a challenge to someone like Bryan.
Punk never keeps the same look and gimmick for long. I could see him being for this storyline if it got him in a Wrestlemania main event which is what he's always dreamed of.
It's hard to believe that he's never main evented a Wrestlemania. He really did deserve it.