The people who are acting like Sonic appearing in Smash Bros is impossible need to wake up and take a look around.
Sega is making Fzero, Namco is making Starfox, Capcom is making Zelda, and a Nintendo developer is making Metal Gear Solid.
The impossible has become commonplace on the Gamecube and Sonic appearing in a Smash Bros sequel is a very real possibility. He might even bring Megaman and Pacman with him.
Because, at this point, it doesn't seem to matter who owns what.