This isn't that great of an idea in my opinion. I'm not saying that all of it is bad, but a lot of the Fan fiction on the internet is usually just crap that goes completely outside the style of the original creator's work. It would just bog down the MB. If you want to show off your fan comics, you can share a link to it in your signature or in General Discussion of Sonic the hedgehog. There's no need for a specific section just for fan fiction or fan characters.
That's just my opinion, though, STD might actually like the idea.