Yo Disch! Good to see you show up on the RH scene again (though I've hardly ever been part of it myself, always sort of lurking at the edge).
You want to make an editor, eh... my first instinct is to suggest that you add a music editor to FF Hackster, but you'd probably find it boring and tedious revisiting that game, whereas I can't keep away from it (even though I'm not working with it at the moment; rather I'm doing a FF Tactics hack).
Hmm... I'm trying to think of decent NES games that don't seem to have editors yet. How about Dragon Warrior III or IV, Battletoads, TMNT II, DuckTales, Little Nemo, Willow, Ninja Gaiden II, Clash at Demonhead, Wizards & Warriors I or II?
If you decide to go SNES, what about one of the Castlevanias? I don't think they have any editors. It would be cool if that 'Dracula X' game could be made into something closer to Rondo of Blood. Super CV IV is more deserving of an editor, though, and would probably inspire better hacks.
Well, whatever you decide to do, just try to have fun with it and don't stress over it