Whenever this conversation comes around I have two answers:
1) Chrono Trigger. Give CT a remake using the Dragon Quest VIII and XI graphics model. 3d Toriyama graphics, since he did the original designs for CT, would be amazing. A nice mix of menu and action controles, and add in full orchestral soundtrack for the game, and it would be videogame ambrosia.
2) Final Fantasy VI. I know VII Remake will be years in the finishing, but with the success of VII Remake, SE needs to do a VI Remake, because if any classic RPG deserves an overhaul and fresh coat of paint it is VI. VI was an incredible story with a great cast of characters.
Honorable Mention: If I’m calling for FF VI to get the Remake Treatment, then I’d want FF VIII to get it as well, because that game doesn’t get enough love.