How about instead of feuding with John Laurinaitis's bodyguard (whether that's A-Train, an FCW powerhouse or someone else entirely) or the next guy to get a big push Cena were to form a tag team with Zack Ryder and chase the tag team titles?
This move would have numerous positives. It would help to keep Cena away from the WWE title picture, which would allow others the chance to shine and prove they belong at the top of the card. The tag team gold would receive an image boost if a star of Cena's standing expressed a desire to win it.
Most importantly Zack Ryder would receive a boost from the revived on-screen association with Cena and appearing in feature storyline. If the creative team were willing to think far enough ahead they could even plan one man turning heel on the other. That would most likely be Ryder turning on Cena, but it's still something fresh isn't it? Were that timed to happen in time for SummerSlam or Survivor Series they could present a fresh bout on what are supposed to be marquee events.
Cena and Ryder's title chase would fit nicely into a couple of months of television. The starting point would obviously need to be a segment (preferably in the ring) in which the two men bury the hatchet regarding the recent Eve Torres storyline. It's easy to imagine Cena suggesting they form a regular duo, though it would be better for him to present it as "I admire your dedication and talent, Zack, and I'd like to work with you" as opposed to "I got nothing else going on right now." Sadly the latter is all too real a possibility.
These two would make a great regular combo
From there the broskis could topple a couple of disposable combos (with Ryder being booked as Cena's equal, or something close to it) before facing the champions on TV in a non-title affair. A win there would set up a pay-per-view clash in which new champions were crowned.
Of course the downside is that there is nowhere obvious to go after that. Not now at any rate. But if WWE introduced two or three new teams while preparing Ryder and Cena for their tag title win, and made use of The Mid-Card Mafia and Hunico and Camacho, then a doubles division could be ready by mid-May.
Anything that gives John Cena something new to do after so long at the top can't be all bad, can it?