I'm not sure having Michaels turn on Bret would be a good idea. I think Bret feuding with Vince rather than Vince and Shawn is better. Bret and Shawn shaking hands was a great moment IMO and should be the end of their rivalry.
Also, I think it'll be two different matches at WM. Cena/Batista and Bret/Vince. I can't see them teaming up Bret and Cena, two guys who've had nothing to do with each other, at WM. It would just come across as a cheap way to get Cena over IMO.
EDIT: On another completely random note, how come Jerry Lawler is sticking up for The Miz recently in his fued with MVP, but no other heels? Except Orton, kind of....