I won't download until I see screenies, but anyways......
I think possibly the best way to make a Sonic Related MMO, is for it to revolve around Chao. Just think of the possibilities!
Chao have 3 different "alliances" Hero, Dark, Neutral, which would offer variety among different classes.
Classes can also be handled like normal Chao breeding in SA1/2, increasing different stats can change appearances, which abilities they can learn, etc.
In SA1/2 you see ads for a movie called Chao in Space 1/2. So, an MMO like this can ALSO, take place in space, giving you multiple Chao planets to explore.
In SA2:B there are Chao who drive mechs, which in turn could make traveling around bigger areas quicker.
And who knows? Maybe the Chao have their own little language they speak, offering the possibilities of side-quests.
Who's with me?