It's no secret that WWE has high hopes for Alexander Rusev. The Bulgarian Bruiser has made a big impact in WWE since he debuted on Raw in a match the night after WrestleMania 30. That followed two full months of his friend Lana saying "nimanye" and then rambling on about how he was going to dominate. If they really want to have him make a big splash then it wouldn't be a bad idea to have him focus on John Cena. It would likely take place after Cena's issues with Bray Wyatt are over, but it's certainly a possibility. Remember when Tensai debuted (as Lord Tensai) one of the first people he targeted was Cena. He even pinned him on Raw two years ago. The point is that WWE has shown in the past that if they really want to push a heel against Cena they're going to do it. Tensai's push didn't last too long, but it will work for Rusev. Cena's value right now is as the biggest legend in WWE that's an active full time performer. They're not going to have him lose too often, but it makes sense for him to work with different people on the roster.