A recent job listing for Microsoft Game Studios' internal team Turn 10, the developer behind Forza Motorsport, indicates that they are gearing up for Natal. The position is for a business development manager who will "drive high quality game content for our Next Generation games including the Natal platform."
So, will Natal be integrated into Forza? Keep in mind that Microsoft isn't ditching the standard controller for Natal, so don't expect dedicated-Natal support. It will likely be for other applications rather than actual gameplay. God forbid they pull something like Mario Kart Wii.