Hey mike, it is not obvious that it will be Green Hill. It seems to me like they will gravitate towards something 3D, as they are currently making a lot more 3D games than 2D ones. SSBB inclusion is a MAJOR selling point, which is why I think Sega would have requested a certain THREE-D stage in to sell their games more effectively. Green Hill may be classic, but it really isn't classic Nintendo, which would be the only reason Sakurai would put it in.
Why would nintendo gravitate towards something 3d? You have to understand the main reason sonic is wanted in Brawl: Sonic vs Mario in the 2d age. Sonic and Mario were rivals, and games like sonic 2 and smb3 were made in an attempt to win the console war. Sonic and Mario's significance together were because of the 2d, genesis games. That's why mario&sonic at the olympics is coming out! The classic rivalry is still in place today! Sure, once sega flunked on console making, they basically sold out to nintendo for making games, but the main reason is because sonic vs mario is a rivalry of ages, and it almost -is- classic nintendo.
Sakurai is not putting a stage in the game to sell a game. SSBB may be a selling point for retro characters of sorts, but sonic doesn't -need- a selling point. Sonic sells on his own, as games like sonic rivals show. Sonic 3d already sells effectively. Including city escape would simply sell used copies of an old game! Putting in an s06 level would disgrace the franchise because it's not iconic. It's clearly going to be a wellknown, wellremembered, well represented stage. Hi, green hill!
Classic nintendo? What? Sonic isn't classic nintendo, unless you call heroes classic. Sonic is a classic, iconic character with close ties to nintendo. If you're going off classic nintendo, please tell me why Shadow Moses Island mae it in for snake? That's classic sony, not classic nintendo.
And, as crowbar pointed out, sonic himself isn't classic nintendo, so you can't really pick a classic nintendo stage for him.
Finally, his 3d games are hardly classic nintendo themselves, so there's no reason sakurai would put one in on the basis of "classic nintendo", either.