I would love:
- a custom level editor/mods for Krusty's Fun House (NES) and the Adventures of Lolo trilogy (NES)
- Adventure Island 4 (NES) remake with support for multiple items in extra buttons like in Ocarina of Time
- Gargoyle's Quest 2 (NES) without the horrid slowdowns
- Megaman Legends (PSX) and Syphon Filter trilogy (PSX) with better controls and bugfixes (SF grenade logic is horrible: may kill you from a kilometer away or ignore you if you're hiding behind a paper-thin object)