I know the idea of mapping hacked games is somewhat iffy on this site, but I had an idea. Rather than making it as a "list of hacks that need to be mapped" that people can pick from, let people pick out a hack they think is worth mapping. That way you don't need to draw the line yourself, just let people choose what hacks are notable enough to map. Have it as a fun little side project rather than make it a big "we must map
everything" type deal.
I think this is a great one to start with: Return to Dinosaur Land, a completely new, yet completely familiar Super Mario World hack, focused entirely on level design rather than gimmicks and custom coding. I have the first world mapped out so far.
http://imgur.com/a/X5gfCLet me know if this is something you'd be interested in! If not, whatever. I'll still make it, it just won't be hosted here.