I'd really like to see someone attemping to make a scary level or even levelpack. It's really difficult to do in JJ2, but I believe it's not impossible. Generally when I say that I think of Metroid Fusion, which really gave me a thrill on the first time I played it. Dark atmosphere, creepy music, narrow corridors... And shock attacks. If someone could manage to pull that off, that would be no doubt the most original JJ2 singleplayer submission.