These are my predictions.
2 new DLC: Likely
GTAnext in 2011: Possible
New GTA on the PS2: Unlikely

I doubt there will be a new GTA for the PS2. It's a dying console that's been around for at least 9 years. Rockstar have already focused on the next-gen consoles and newer consoles and handhelds, as we all obviously know. The next GTA in 2011 I think may be possible, Rockstar rarely leaves big gaps between games. The two new DLC I think is likely because as FB has stated numerous times,

quote Final Blade

_{As for the next disc medium, I don't think we'll be seeing any for another 4 years or so, since they're apparent on whoring out GTA DLC to it's max. Which lets face it, not only is it cheaper to produce, they'll gain more money in the long run.}