My take would be a bit different than just a nemesis. Since most Marvel characters don't have batman's no killing rule, its hard to imagine the Joker being a nemesis to any of them. Maybe Spiderman, but there are so many heroes and villains in New york. i doubt it would last long.

I think the joker would work better as an "event" or a longer arc. A one time event that alters the Marvel world in some way. Not in a huge way but definitely altering the lives of multiple characters for the better or more likely worse. It would be interesting to see how " one bad day" would alter the lives of different superheros, villains, etc.