Vince McMahon is on his annual kick of trying to sign former talent to the company. Vince gets on these kicks because feels he needs more talent. Rumor has it he has had inquires sent out to CM Punk, Rey Mysterio, and John Morrison. Details on each case are very skewed to say the least. as really only Vince knows as he is keeping things close to the vest.
Morrison is currently upset with AAA over the handling of his fiancee, and its likely the Lucha Underground contracts are going to become dissolved soon.
I have no information on the Rey situation other than he wants one last run in the states. (UPDATE - Sources say talks with Rey heated up over the weekend. Both sides discussed terms and monetary value.)
As far as Punk goes, you never say never in this business. As much as Punk has said he does not want to wrestle again, and never will in WWE, if he and Vince can come to terms on the lawsuit and solving that first, I don't see it being out of the question. However, I will believe it when I see it.
At the end of the day, Punk is not getting any younger, and there is a lot of money he could be making if he chose to return.