A Final Fantasy- Oh wait.
A Star Fox MMO would be rather neat. Design your own character and ship. Join a team, get a command ship, and do missions across the galaxy, perhaps having the option of both ground and air travel. Have the controls set up in a sort of flight sim fashion, perhaps even allowing for joystick compatibility.
Character-wise, there would probably be the most common races available (Dogs, cats, foxes, wolves, birds, throw in humans for the hell of it), but on top of that you would have a homeworld or territory alignment (Cornerian, Katinan, Saurian, etc.). I would also stick Cerenians in there, though the backstory on them would need to be expanded (seeing as they only get a brief mention in the Adventures manual). PvP wouldn't be depending on faction, and would pretty much be free-for-all so long as your target is flagged. It's a rough world of mercenaries, after all.
While there wouldn't be any classes, you could pick a focus in either ground or air-based combat (giving you a bonus to one set of skills and a penalty to the other), or a mix between the two (with no bonus or penalty to skills). There would be a renown system (pretty much a level system) that would allow you to add on to your abilities with each rank or so. There would probably be sub-jobs as well (mining, hunting, delivery, ruin exploration).
Fighter ships would probably abide by a set of three tiers: Fast, balanced, and heavy, with specific parts for each variety (much like Phantom Crash, if anyone's ever played that). There might also be specific manufacturers, each with their own company-specific and unique weapon.
Buying things would depend on renown, money, and ship class (ie. An average player with a decent amount of money and a fast fighter couldn't buy an elite expensive uber-cannon designed for heavy ships.). The same would apply to guns for ground missions.
In theory it would be great, sort of a combination of EVE Online (only more eventful) and a Sci-fi themed ground MMO. Of course, the production team would undoubtedly do something to make it go tits up, though.
And you know there would be furries there. Not that that's a bad thing, mind you.