If I had the tools and talent to do fan editing, I think I would start out by trying to make a movie or series of the Arrow Island Flashbacks to see how it flows. If I was trying to do something more creative and involving, then I would go through all the seasons of the simpsons, and take every flashback of "young homer"'s life and try to put them together chronologically and thematically to make a coherent movie out of it all.
I can't watch Ash vs Evil Dead without wondering how a streamlined version without end credits and side trips would work out. Removing most of the female cop's role and a lot of the early side quest to the other girl's parents house and cutting it together more like a movie could be a fun watch. I'm sure some one has already done it, but I would love to see the original evil dead trilogy cut more coherently together without internal contradictions lol.
Hrmm, what else. lol.