Personally I've no interest in it at this point as their is no motivation. What's the cause. Why would either want to have the match with the other? There are others that would benefit more from a Lesnar feud that would make more sense.
True there are others who could use that rub more than Punk, but I think the fued can easily make sense. Punk returns and assumes business will return to usual because he's still one of Heyman's guys. He's taken time off to think and heal, now Paul's gonna help him get that title back.
... Except that Paul isn't interested in Punk anymore, after such a big loss to The undertaker, two to The Rock and all the shenanigans needed to keep Punk the champion. So when Punk comes knocking, Heyman decides he isn't worth it and dumps his stock, knowing Lesnar is more dependable and likely to win the championship. The Lesnar/Punk fued is pretty easy to set up from here, possibly by costing Brock a title match or getting in his business.
It echoes what Mick Foley said to Punk when he was first getting involved with Heyman, something like: "At the end of the day, Paul Heyman is just doing what's best for Paul Heyman". It's pretty easy to book, it's a fresh scenario, it shouldn't be hard to schedule, the matches and promos should be decent at least and it leaves the title scene with John Cena wide open for whoever else they want to push. Anything involving Cena and a title is guaranteed to main event anyway.
I know it isn't what some people want or are particularly interested in, but there's definately a solid foundation for it work and it couldn't be worse than a lot of the other possibilities.
