Thought I'd go over the various racing series and see/speculate what is feasible and what isn't going forward.
F1
Current cars in game: RA272, MP4/4 (F1500T-A is a legally distinct Lotus 97T as well)
Licenced?: By EA (F1 24)
Future prospects: As we know, F1 generally allow one modern-ish car to go to non-licensed games along with historic stuff, such as the Merc in GTS. Worth noting GT are no longer on Hamilton's cap, so there's not an obvious team that screams out "they have a relationship with PD" anymore.
WEC Hypercars (LMH/LMDh)
Current cars in game: GR010
Latest cars not in game: 499P, 9X8, V.Series, 963, M Hybrid
Licensed?: By Motorsport Games (Le Mans Ultimate)
Future prospects: For LMH - the GR010 in GT7 is, to my knowledge, currently the only LMH in a sim outside of Le Mans Ultimate. That means these could pretty tightly locked down license wise, though a lot of them are also pretty new to be fair. LMDh seems a lot more free - the Cadillac is in all of Forza, iRacing and AMS2, and the BMW and Porsche are also in iRacing, and we know PD and IMSA are on okay terms.
LM top class endurance (Group C to LMP1)
Current cars in game: XJR-9, 787B, Sauber C9, R92CP, 962 C, BMW McLaren F1 GTR, CLK-LM, 908 HDI, R18, R18 TDI, TS030, TS050, GT-R LM Nismo, 919
Licensed?: No
Future prospects: Mainly putting this here to acknowledge people want the TS020. The early 00's are the hole in what is otherwise a very well covered list. There's also a bunch of pre-Group C cars but my knowledge of which cars those are exactly is patchy.
Indycar
Current cars in game: None
Licensed?: By iRacing (Game TBA)
Future prospects: Not happening, they're very happy to be back with iRacing after the Motorsport Games debacle.
NASCAR
Current cars in game: None
Licensed?: By iRacing (Game TBA)
Future prospects: Not happening, they're also very happy to be back with iRacing after the Motorsport Games debacle. I could see a world with a generic GT stock car being added for GT8's launch, though.
Super Formula
Current cars in game: SF19, SF23
Latest cars not in game: None
Licensed?: No
Future prospects: They have the cars. The only question is whether Fraga being in Lights last year is enough for the Lights car (iRacing just added it, they also have the full fat SF23).
WRC
Current cars in game: 205 T16, Celica ST205
Latest cars not in game: GR Yaris Rally1, i20N Rally1, Puma Rally1
Licensed?: By EA (EA SPORTS WRC)
Future prospects: Modern rally cars don't really show up outside of the licensed series, so I think the only way we see a Rally1 car is if Toyota really want the Yaris here for some reason. Historic rally cars are possible as seen with the Celica being added. There is the open question here of course of how committed PD are to off-roading of any kind.
Super GT
Current cars in game: '97 Supra GT500, '99 GT-R GT500, 3x '08 GT500s, 3x '16 GT500s, '21 BRZ GT300, '23 RC F GT3 ANEST IWATA
Latest cars not in game: Z GT500, GR Supra GT500, Civic Type R-GT
Licensed?: No
Future prospects: If you believe in patterns, 8+8=16 and 16+8=24, so clearly we're getting the '24 GT500s, right? The relationship here is definitely still at least fine, as we can see by them getting Fraga's Lexus in the game last year, so there's reason to be optimistic on this one I think. I imagine lots of people also want the turn of the century NSX GT500 to complete that trio.
GT3
Current cars in game: A lot. Most recent are 2018 GT-R GT3, 2019 R8 LMS Evo, 2020 AMG GT3
Latest cars not in game: M4 GT3, 296 GT3, 720S GT3, 992 GT3 R, Corvette Z06 GT3 (probably not happening since it's Pratt & Miller)
Licensed?: By Kunos Simulazioni (Assetto Corsa Competizione) - other GT3 championships do exist though
Future prospects: Obviously, very highly requested by a lot of people. My completely unsubstantiated theory here is that PD might be having some trouble with licensing liveries from the individual teams. Because GT3 cars are customer cars, you need licensing from both the manufacturer (to get the car) and the team (to get the livery) if you want a race liveried car. And the most recent ones we've had in GT7 (R8 Evo, AMG Evo, '18 GT-R) have all either had their manufacturer launch livery or a fantasy livery. Maybe something in the ACC contract? I don't know, just speculating. Doesn't seem to hurt iRacing, but I think the team there are closer to the real life teams.