I love Forza 2, but here is my 2 cents worth of ideas for Turn 10's next project:
1. Paddocks/Pits on every track.
2. Real world tracks only.
3. More gaming community friendly. (Something like in Test Drive Unlimited, but allow clubs to have their on place to schedule races and tournaments.)
4. Allow racers to be able to customize their on garage with personal team name, number, colors, etc.. (Example: Warlord Racing #777)
5. Hook up with a network like SPEED VISION and offer recent races for small fee. Like the American Le Mans, Suzuki Super Bike Showndown, F1, SCCA, NASA, NASCAR, WERA, HSR, and SVRA.
6. FLAGS!!! I haven't seen any race without them. Even if it doesn't slow the race, at least it would inform us that something is going on down the track and it would inform us that we are doing something illegal to the race rules. It would also be nice to see a checkered at the end of a race.
7. Co-op tuning rooms. So you can get assistance from a friend to help trouble shoot a problem.
8. This might be a biggie, but I would like to save a replay and some how be able to download it to send to a friend to watch via e-mail. This would also probably help recruit new Forza fans. People that never would have heard of Forza could be tempted by a video from a friend. Marketing man, marketing. lol
9. Weather. I purchased Road Atlanta tickets for the American Le Mans in October 2008 (Forza helped with the interested in the Le Mans.), there is a chance it will be raining or very cold to camp out, but they will be racing no matter what. Forza needs a random weather option, with tire swap option too.
When someone says simulation, that is the point of some of the ideas above.
Edit: Almost forgot, 10. Qualifying.
"All I need is a 440 six pack!"
Warlord Racing #777