It is not that bad really. Similar things have happened before.
Recall Soul Calibur for GameCube? Nintento let Namco get their hands on Link. Nintendo let Capcom get their hands on Link for the GameBoy games, and let's be honest, those were amazing.
In all honesty, if I see Sonic in non-Sega games, I pray to the great Swirl they are Nintendo made. At least we know with Nintendo the game will be what it should be, Sonic will move and act like Sonic, and he will be treated with respect. He was, after all, a fearsome opponent for many years, and they owe him that much.
Now if Sonic were in M$ first party titles, I would be afraid he would need a "XBOX 360 patch 0.987.1f" before he could run at speed, and then he would have a blinking red ring of death that made him unable to take any action until you shipped his little blue butt back to Redmond for a 2 month vacation...