Cena will lose to Reigns. Cena will be champion and Reigns will be the Rumble winner, and it will be atrociously bad. Beyond that, I have no clue what will happen.
What I'd love to actually see would be Bray Wyatt as the WWE Champion facing Taker and breaking the streak, but that's wholly unrealistic, sadly.
Don't think we're gonna see Rock back, and just as well, for my taste.
Could see Bryan vs Lesnar but that might be at SummerSlam this year. Either way I'm betting we get that match in the next year.