Maybe they could re-do the Sonic 2 levels just so that the graphics were the same as those in Sonic 3. They could maybe slightly alter Death Egg Zone of Sonic 2 just so that you get rings, just because of the annoyance of fighting two bosses with no rings so early in the game (like the boss levels of Sonic 1 and 2 Game Gear).
There would definitely need to be a save function as well.
17 December 2009: I shook hands with the Lord Mayor!
Actually it is. Media Molecule has it on there web page. They said "Please don't send us any ideas for new games, because it would be illegal for us to use it." or something similar. Our only chance is if a good hacker would make this for us. I've got some more details too!
The amount of development involved for what has been described is way too much for one "hacker" to do. It requires development kits and a lot of design, animation and coding. And they'd be able to make the game if whoever created the idea released all ownership of the idea to them.
"Any society that would sacrifice a little liberty to gain a little security will deserve neither, and lose both"-Benjamin Franklin