JK. If they do decide to do a 3rd match, Summerslam would make a ton of sense. That said, with two massive stars like the Rock and Cena - I could see Vince happily ending their feud with an 'everyone's-happy' 1-1. I picture a handshake after Mania 29, and tie a ribbon on the feud.
Maybe this is a question for another thread, but if its Taker vs Cena & Punk vs Austin at 30... who does the Rock fight? Hopefully an up and comer - I'd prefer it to be against The Dazzler - Daniel Bryan - with a new clean look and a Ric Flair robe.