I'd like to see something akin to Super Mario All-Stars.. using the first three games and maybe the gameboy titles as well (using the original designs for the sprite updates, including Simon's CV1 and CV2 costumes from the NES box covers), but there should be a lot of added content:
Give Simon's Quest additional dungeons to unlock, and put a level editor into CV1. Unlock various artwork and design notes from the games. Unlock various CV characters (Richter, Alucard, Simon's CV1 and CV2 costumes etc) for play in any of the games (simply as a bonus).. and then even have a character editor, so you can set your own traits (like backflip jump, dash, doublejump) to any character.
It's a pipe dream, but I've been thinking of that for a long time.