Update: Nintendo has added the game to its website and like the other games in the Sega 3D Classics line it’s $5.99!
Well, it’s a little later than planned (they just said September), but not by that much. 😛
The 3DS version actually has a wireless co-op multiplayer feature where one player is Sonic, and the other is an invincible version of Tails to assist Sonic in the game, basically like you did on the TV back in the day. You’re also able to save at anytime and can now more easily unlock Super Sonic just by beating the game on any mode, which gives Sonic all the chaos emeralds when the feature is turned on.
Sadly at the moment there’s no release date yet for Europe.