Although IGN had this interview on their IGN Insider, they have released the interview to the public! check it out.
IGNDC: Will there be online features for Sonic Adventure 2?
TI: Right now we're still in the planning stages of our online features, and while it hasn't been completed yet, basically the player will play the game and once they complete a stage or level, they'll receive a certain ranking. And through the Internet, they'll be able to upload their score and see how he ranks against other players on a worldwide basis.
IGNDC: Having played through the game numerous times, we've been able to see the big changes in Sonic Adventure 2 in terms of the faster gameplay and improved frame rate. What other major improvements have been made in Sonic Adventure 2 over Sonic Adventure?
TI: (laughs) There are so many, it's pretty hard to answer that. Obviously we wanted to make Sonic Adventure 2 run at 60 frames per second and design the stages so that when you play the game, you feel like you're going a lot faster. And then, the two-player versus modes was the next big benchmark after we established the 60 frames per second.
And for the future of Sonic's actions, instead of blazingly running through a stage, we've given him more actions so he's not just constantly running. So he'll run, he'll grind on a rail, then he'll spin dash into an obstacle, etc. It's not just about running fast; we wanted to create a "tempo" for the action.
IGNDC: Speaking of the two-player mode, right now in our preview version, there are three versus games – Sonic Vs, Shadow, Tails Vs. Dr. Eggman, and Knuckles Vs. Rouge. Are there any more mini-games planned and will other characters be able to battle each other (i.e. Sonic Vs Tails)?
TI: Ahh... well, that's your preview version (smiles). For that preview version, we've only included one stage per versus game. With the full version, you'll see a lot more stages for each versus mode. I really can't say too much about the versus games yet, but there are two other versus modes we're thinking about incorporating outside of the three that you've played.
IGNDC's full interview