Kaizo Wario Land 4 would be interesting.
But we don't have a Wario Land 4 editor.
Somebody should make it. And hopefully make it better than the 1/2/3 editors...
Wario Land 4 has some levels with insanely hard to use tileset, likes Mystic Lake, Arabian Night, Fiery Cavern, etc.
And I suspect getting the bosses to change in any way would be ridiculous in this game. You could at least create a new Wario Land 2 or 3 boss room fairly easily, since the opponents are small with simple attack patterns.
Ohhhh I just noticed that something's missing from the Golden Diva sprite sheet (the one by Gussprint): The face she makes when you fall into the floor spikes. It's another hilarious expression which sadly most players will not see.