The obvious set up to me and others has to do with the rumors of Brock winning the world title again later in the year. If Brock wins a belt and Punk returns and wants the title, then the feud is set up. From there on, perhaps Heyman is forced to choose between the two of them and goes with Brock OR Brock attacks Punk before that can happen and then Punk roundhouse kicks Heyman when he tries one time too many to stop him from going after Brock for revenge. I have a few different ideas on how this could be booked.
The interesting thing is that Brock might be winning the WHC instead of the WWE Title. Brock putting the replica of the WHC on his shoulder while ripping the office apart on Raw was probably foreshadowing (him staring at The Rock's poster certainly was, why not this?), which is interesting since it means one part timer wins one world title, the other wins the other. It also means that Brock's title defenses and feuds could be a semi main event, instead of the headline so people should be a lot less annoyed if Brock misses a show here or there as world champ.
Punk could return earlier than expected and win the MITB briefcase for the WHC while Brock is champ OR Punk could return while Brock is already champ and say that he made history with his long WWE Title reign and now he wants to do the same with the WHC, which Brock just happens to hold. I like the second option better.