I know what your thinking:
THERE WILL NEVER BE A SONIC MMO. A WORLD FULL OF SUPER-FAST HEDGEHOGS DOESN'T MAKE SENCE!!!!
You finished? Here my idea for a good Sonic the Hedgehog Online!!!
Ok first of all, you will not be a hedgehog, you will be a human. You have to raise chaos for battle. This closely resembles Neopets only way better.
Now your asking: Besides chaos, what does the game have to do with Sonic?
You will be Sonic and all other characters (including Tails, Knuckles, Amy, Cream, Big, Rouge, Shadow, Espio, Charmy, Tikal, and Vector). You will be these characters in 1p mission (meaning only you are in them and the only things moving are NPCs and you in the mission) for rings to buy things for your chao. You see other players as you walk around adventure-fields (yes thats off Sonic Adventure DX). In the adventure fields you can find portals for you to go to the missions.
In the game you can have your very own chao garden, using ring to buy diffrent landscapes, more room, and other things (like swings or a rock). As your chao progresses, it will turn into a hero chao or a evil chao depending on how you raised it. Also, you can get more chao eggs by letting your chao mate with someone elses chao, or buying a new egg.
Does that sound like fun or what?