I tend not to play fantasy booker, but I think I have a pretty good, if not, fun idea for the summer angle.
CM Punk and Brock Lesnar have Paul Heyman as their manager and it leads to the inevitable dissension between the two as they fight for sole control of Heyman's managerial services. Both Lesnar and Punk should remain as a heel to keep Punk's nasty edge, for reasons you're about to see.
At Summerslam, Punk & Lesnar face off in a No DQ match for the WWE Championship with Paul Heyman as special guest referee. They both go at each other in a brutal match where its tick for tack for almost the entirety of the match. Punk goes to pin Lesnar, and Heyman tries to screw him with a slow count. Punk starts to put the fear of God into Heyman by getting up close to him, talking trash, maybe even beat him a little. Punk then gets back to Lesnar, brutally beats him and Heyman reluctantly counts the pin 1-2-3.
Next night on Raw, CM Punk comes out with Heyman and proceeds to verbally assault him and threatens to make his life hell if Heyman ever tries to cross him again. They continue on for a month or 2 with Heyman reluctantly helping CM Punk win his matches.
Punk now has merit to those claims that he's the "most dangerous man in the locker room" with a violent beating of Brock Lesnar in their match and he has the chance to get reeeally over with the mainstream fans that tune in to watch Lesnar and see Punk as a legitimate badass.
Maybe a little too internet-fan-friendly, but hey, so was booking CM Punk to hold the title for 434 days