Potentially controversial opinion but I don't even think John Cena will get the same kind of nostalgia pops from crowds 10 years from now when he is trotted out for some random raw (assuming Cena has retired by then). At least, compared to say, what would happen if The Rock or Austin showed up on Raw next week.
A wrinkled up Cena standing at the top of the ramp as he looks into the camera "Hey, you still work here?" he says with a wink and a laugh. Salutes and as soon as he's about to take off down the ramp, he acts like he pulled a hip, laughs it off a little and jets down to the ring.
You're crazy if you don't think crowds wont still be chanting LETS GO CENA. CENA SUCKS. When he's 60 years old "Never change WWE universe, haha. I came out here every Monday and even twenty or so odd years later, you still pay good money to come out here and chant whatever you want. Ya gotta love this business..."
Cena is INGRAINED in WWE. All these little kids, the Cenation will be in their 20-early 30s. Reminiscing about the good old days.
Cena has done more for the company and it's image more than Rock, Austin and eventually even Hulk. And you don't have to believe me, time will provide my evidence. You don't have to like it, but you sure as hell better accept it, jack.