Well Punk and Austin are supposed to be pretty good friends. Austin's been away from the ring for quite some time so maybe his injuries might have healed up enough for 1 last match and Punk is a good enough worker that he'd be able to protect Austin from any sloppy moves that could hurt him.
Would like to see Austin Vs Punk at WM. It'd be a good match and it'd give Austin that old icon vs new icon match that he missed out on when Hogan came back and faced Rock.