I suspect T10 will struggle, though.
- F1 cars are licensed by Codemasters F1 series. F1 2023 has all the current cars and tracks, obviously.
- Le Mans cars are being licensed by "Le Mans Ultimate", which will include the full current WEC cars (hypercars, prototypes and GTLM) and tracks (built on rFactor, proper sim).
- GT3 and GT4 cars are licensed in "Assetto Corsa Competizione", which includes all the GT World Challenge and Intercontinental GT car and track lists (also a proper sim) and has clear links to the SRO which organises these car series worldwide. This includes 13 different GT3 manufacturers and 11 different GT4 manufacturers, and has been updated with brand new 2023 GT3 models such as the new Ferrari 296 GT3.
- NASCAR is still being licensed and delivered by NASCAR heat series.
So yeah, Forza probably can't negotiate blanket licenses with these major racing series and would have to license each car individually. Which means we will be hard pressed to get full modern fields.
Edit: Not all race series are being licensed. I don't think anyone is currently making a TCR/WTCR game, so that might be an easier one to get for Forza.