Confirmed features:
-Day to night transitions
-Kart racing
-Car model damage
-Dynamic Weather
-Track editor
-1,000 + cars (no Porsche, sadly)
-WRC (will include co-driver and point to point rallys), NASCAR, Super GT.
-Top Gear test track!

Things that concern me are whether the game will be able to run at a consistent 60fps with weather effects. Rally physics in the past games have been so lackluster and feel strange. Engine, exhaust, and gearbox sound have been terrible in the past (or poorly mixed) and hopefully see even more improvement over the GT Time Trial build.