My main concern around this match, is Rock's ring rust.
If Rocky doesn't wrestle in front of a crowd from now until then, I see him stumbling a bit. Even the best needs practice, Hogan was still a semi-active competitor when he faced Rocky back then, and Hogan wrestles a very slow style which works for him. If Vince expects the Rock coming out, doing an eyebrow, getting a Rock bottom reversed into an STFU and an epic tapout to break a million buys, I'm missing the appeal.
Cena will be a legend. He could retire tomorrow, and he has a for sure first round hall of fame and legends contract, he's been (arguably) WWE's top draw for half a decade.
If Cena/Rocky can toss on a finisher spam Undertaker/HBK style match, they'll get some reactions, but I think Hogan/Rock eclipses it by a mile. The audience has evolved over the past decade, IWC or not, and fans are too in the know to mark out as bad as they did for WM 18.
Rock gets cheered, even if he sets a bus full of orphans on fire the night before. Cena get's booed because he's Cena. Cena doesn't have the fans attention and respect anywhere near as much as Rocky did 10 years ago.