I'm not saying that Lesnar and Rollins have a feud, what I'm saying is Rollins should turn on Lesnar at either the Rumble and cash in the MITB, hereby becoming the WWE champ, heading into Wrestlemania.
Let's face it, Lesnar is leaving after Mania, so whoever he has a match with at the biggest show of the year, you're pretty much guaranteed that the challenger is going to win. How about Rollins and Reigns being that match instead, they you're not guaranteed that Reigns will win. Just cause he wins the Rumble he still has to get through Rollins for the title. Now he has beat him clean in the past, but I don't expect that to happen this time.
It would put one hell of a swerve into this that no one would see coming. Fans would be overjoyed that someone is holding the belt that actually shows up for work each week.
It's just a thought.
I don't mind the scenario at all....however, I have been having a feeling that perhaps, John Cena will go over Brock at the Rumble and end up being the one to face Reigns at WrestleMania instead.
IF Reigns vs Cena were to happen, I am sure that would add unpredictability to the Main Event and still, the cash-in scenario can happen anyways.
On your scenario above... I wouldn't mind it happening as it would indeed be fresh. But, as I pointed out, personally I don't think either Reigns or Rollins are big enough to be headlining Mania without an established name alongside them, though I'd gladly be proven wrong on that one.
All that said; the biggest swerve possible, though it would require brilliant writing that has been well thought out for a while, is having a totally different Royal Rumble winner than Reigns unlike last year where Batista was rumoured and though it was unpopular, the WWE went through with it anyways... Only problem is, bar a Daniel Bryan unlikely surprise, I just can't think of an alternative to Reigns that makes total sense based on booking...