I think they should hold back on turning punk heel.... Have him change brands first and continue to get over as a baby-face (albeit with a bigger weekly audience) so that when the time comes your average fan will hate him, rather than still having half the crowd likeing cos he's still a good wrestler. When the time come have him massively double-cross, and fued with, one of the 'forever babyfaces' like HBK or Rey.
Like I say, no rush.... Like Cena or Hogan or similar I currently see Punk as bonafide BABY face and as with those guys, done at the right time a heel turn could be huge!
Besides, I still wanna see him in a multi-match fued with Edge (One of the main reasons I hope they have Edge regain the WHC @ Backlash once the Deadman's gone 16-0 @ WM.)
Would also love to see him vs Orton which would also be better with Punk as a face, but that'd mean him going to Raw and I think he's destined to go to SD first, albeit rapidly ascending to Raw.