I don't know...
I'm sure any full-sized map of any GOOD Super Metroid hack would be impressive...but that opens a whole can of worms if I were to start accepting maps of any hacks. I wouldn't want to crowd up the main listings, and if I put a separate listing, well I don't know, that's going to get messy, isn't it?
Just because someone has the tools to remap an existing game, doesn't make them a good game designer. And even if one were to justify that some hacks are good, where does one draw the line for what to accept and what not to, because there are certainly a lot of hacks that aren't good. Would anyone really want to accept maps for potentially tens of thousands of only slightly-modified games? At least with games that have come out mass-produced on cartridges in the era of the console it's intended, even when those games are crap, they're recognized as being part of an official library, and are much more relevant than even the best hacks.
I've always thought the point of hacking a game (or making a fangame or something along those lines, like VGMaps's April Fool's jokes) are more meant to teach the amateur gamemaker about how to make games, than for serious release and recognition.
I don't wish to discourage you if you think something is worth mapping. There may be other sites willing to post it, but at this time, VGMaps.com won't. I suppose that'd be an idea if someone wants to make another screenshot map site - one dedicated to hacks and fangames.