I don't think that there will be any message board stuff on GT4. With the amount of stuff that people write on these things, your thumbs would get really tired if you had to do it with a controller!
So I guess it's safe to say that GTP will definetly still be around once the game is released.
One thing that I think PD should really take a good look at is, Gamshark. If there's going to be real online racing, then there are going to be cheaters with it. That means that PD has to come up with a really good built-in rules system. Which limits such things as power, torque, weight, etc. One thing that they might have a problem with is downforce. You can change the downforce of a car in GT3, with the use of Interact products, to make it handle extremely well. Even F1 like handeling. I'm sure that the good people at Interact, and Gameshark users from all over will come up with similar codes for GT4. PD will definetly have to come up with something to combat this, or else the online racing thing is going straight to hell in a handbag, marked Interact.
PS Supra4eva, I thought that the race modification option was the ****!! I really hope that they bring that back.
PSS I also think that there's a pattern. GT1 - started series on a new system, not too many cars. GT2 - perfected the game for PS, lots of cars, GT3 - started series on a new system, not too many cars, GT4 - perfected the game for PS2, lots of cars?
I want more cars, danm it!