The reality is, it might be quite simple to convert an SD 3D game into an HD one.
Emulators already do it, though I'd think SE would put more into it than JUST upping resolution.
Hmmm.... Maybe they'll throw in a brand new super dungeon filled with encounters that takes 5 minutes to beat a piece and loot that's only barely any stronger than the endgame gear found in the vanilla version yet still not any stronger than the still best gear from said vanilla version while the dungeon itself will either consist of a bunch of random assets thrown together to make this overly complicated/ROM Hacky dungeon, or consist entirely of the same room over and over again in a constant boss rush including brand new enemies 80 floors in with gimmicks that will likely oneshot you and make you waste all the hours, menial effort, and lucky loot drops you burnt on it (or maybe Squeenix will splurge on effort and do both).