I wonder if there'd be much issue with licensing stuff like DPi cars, or the upcoming LMDh cars in the future? Those two groups could be excellent ways to get more Gr.1 cars, especially for manufacturers like Chevrolet and Cadillac. And that's just DPi, let alone what LMDh might hold as far as manufacturers go. For example, Ferrari is confirmed to be joining LMDh, and that would be a perfect way for Ferrari to have Gr.1 car, as the only possible alternative would be the 333SP. Overall, LMDh (and to a similar extent, DPi) could provide some much more contemporary Gr.1 cars. BMW is another example, with potential plans for LMDh, and the older V12 LMR as a potential Gr.1 car at the moment. Not to mention manufacturers that seemingly never have had a car that'd seem good for Gr.1, as Lexus and McLaren are some of the other automakers eyeing LMDh. (McLaren VGT aside, that is.)
EDIT: Also, I think we're largely good on Group C racers, though I might add the Toyota TS010 for heritage's sake, and the Alfa Romeo SE048SP so that Alfa Romeo can have a Gr.1 car. The Lamborghini Countach QVX could be nice, too, and if the Lamborghini VGT ends up in Gr.1, then the Countach QVX could compliment the VGT well, as an older Gr.1 racer. On the other hand, I don't think we need the Peugeot 905, though I'd welcome it if it were added, as it's a predecessor to the modern 908 and the upcoming 9X8. But other than that, I don't think much else pops out within Group C as being must-haves. I honestly think the TS010 is more relevant than the 88C-V, too, doubly so with the TS050's success at the LM24, and the new successor to that, the GR010.
EDIT2: I'm also very much looking forward to what sort of made-for-game racers PD ends up crafting, to either circumvent licensing costs for a given series, give automakers representation in a given class, or both. I could definitely see this happening in order to have more Gr.2 cars, given that DTM seems to be licensing hassle. It could be a great opportunity to have racecars in a similar style, but based on models that never were the basis for real-world racers. So for example, I know that in DTM, BMW has the M3/M4/etc., right? But if PD made their own Gr.2 cars, maybe we could see something like a DTM-styled car based on the BMW Z4 (G89), or the M8 (G15). I think it's very possible, considering that the Mitsubishi Lancer Evolution Final Edition Gr.3 and Subaru WRX STI Gr.3 have striking similarities to Super GT300 cars.