Genesis is very unlikely to make an appearance in FF7R, unless they redesign him entirely. Why? Because the use of his character is tied to a licensing agreement with the Japanese Pop-star Gackt, whom Genesis was modeled after. That agreement has expired, which is the reason why CC is not being digitally distributed for PSP and PSVita, and we aren't going to be seeing any HD version of it anywhere else either.
Reviving Aerith is pointless though. As everybody has said ad nauseum, Aerith's death is tied to the story, and even if it would be "fun" to have her reviewed, outside of as an oddity, or as a cheat, giving her a proper revival would and actually tying it into the story would just really cheapen the story overall IMO.
As for things they should add? I can't think of any myths or rumors I'd want them to add. Most of them were pretty dumb to my mind - after all, they were the machinations of silly kids for the most parts, who were just trying to impress or fool each-other.
What I would like to add though -
Lots and lots of side-quests to flesh out character-relationships, or just make the adventure last longer, without messing with the original story.