I honestly would be intrigued by a non-title Reigns/Cena match. Hell, the "torch pass" doesn't need to effectively start with a title win, although that's usually the right way to do it.
And I wouldn't have Reigns win either. I honestly think having a quality competitive match where Cena wins just by the skin of his teeth sets up a good rematch or rivalry down the road, if Reigns does win the title. Cena can always claim Reigns hasn't made it yet.
And guess what? If by some means the match is a total stinker due to Reigns, the office can yank his push without any consequences of a lame champion. The last thing I want is 2004 Orton again.