You can't really bring him back as a heel and make someone, he's gonna be an overwhelming face for at least a year no matter what. So with that in mind I bring him back to say "Everything I said 8 years ago was right, and it looks like they did give the doofus son in law more control, and look at the results", cue HHH.
"Punk, we brought you back after you got your failures outside of here in part because I feel sorry for you, partly to please some hardcore internet fans, and partly because we're trying to avoid you entertaining certain other endeavors. But make no mistake; this isn't your final chance to fulfill that goal that you whined to those internet fans about of main eventing Wrestlemania. You're not a big enough star and don't look the part for us to do whatever we can to put you in that position, and obviously we've seen that you're not tough enough to win it without our help." Punk vs HHH at Mania.
Reigns would make a great heel champ for him to face, but now that they've finally mostly succeeded at getting Reigns over as a face, that would be a big setback for Reigns. And Reigns vs Punk would turn Reigns heel again even f he didn't actually turn in storyline.