Following the news and rumors of Tails maybe or maybe not showing up in SA2, I have run across the ODCM (Official Dreamcast Magazine) and this is something that they have just reported about SA2:
"Although only a few characters have been revealed so far (Sonic, Knuckles, and Dr. Robotnik), sources tell us that five new characters, pulled from former Sonic games on Genesis, Game Gear, amd arcade platforms, will also join the party-introducing new styles of game play in the process."
This could mean that Ray, Mighty, Nack, Espio, Vector, Charmy, Bean, Bark and other Sonic characters who haven't been seen for many years could make a comeback.
Another thing to note, ODCM has also announced that the release date has been pushed back until Fall of 2001. The reason for this being is because Sonic Team wanted to ensure that the Sonic Team would have enough time to make the game everything that they wanted it to be.
Source: ODCM (Official Dreamcast Magazine)