Wishful Thinking: Y2J!
Logic: Since he's Chris Jericho, we'll start with him. Although he is currently involved in other endeavors, Jericho has always been open to returning, In fact, there are numerous reports of his potential return. As far as I'm concerned, it's a matter of when, not if. That 'when' may be very soon.
My choice of Del Rio here does warrant a few answers. You may ask why he still has the strap up to this point. To that I say, why not? The WWE Title is supposed to be the most coveted prize in the history of this business. Instead, it has become nothing less than a prop over the last handful of months. It has been paraded around more than Kelly Kelly in the locker room. The only way to bring it's glory back is to keep it on someone for a while.
You may also ask, why does it have to be Del Rio? And to that I say again, why not? The company currently lacks any sort of variety in their championship picture. It's John Cena, Randy Orton, and _______. Given Mark Henry has made quite the push, it's still a very thin group. Del Rio can work a mic, he's more than decent in the ring, and he could become a very solid heel in the WWE.
Build-up: For Del Rio, he can just hold the strap until 'Mania. He can engage in a few feuds with the likes of CM Punk and John Cena and retain the belt by the skin of his teeth each time.
For Jericho, well, that's another story. I would have Y2J return at the Royal Rumble and end up winning the traditional match, earning him a title shot at 'Mania. He would immediately peg Del Rio and his WWE Title as his target. And just as he did with his WWE debut and return in 2007, he can run a "Save Us" angle against ADR. (He "saved" us from The Rock in his debut and Orton in his return.)