I wouldn't be surprised if "Group racing" ended in a future update and car classes just become "GT3", "GT4" and "Touring Cars"
Considering people have taken issue regarding mixing of cars in racing classess...
I don't see that happening until GT8 though.
Honestly, I have a feeling that the restrictiveness of the Group system is a key part of why we've had a lack of new race cars.
If you think about it, the system was built along the lines of current classes being run at GT Sport's release:
Gr.1 - LMP1
Gr.3 - GT3 Equivalent
Gr.4 - GT4/TCR
Group 2 wasn't even a thing at launch, but eventually was modern GT500's
BUT, this system, while it worked when every car was either built to these regs IRL, or by Polyphony, doesn't work anymore with GT7's emphasis on more vehicle variety.
For starters, older cars like the GR.3 JGTC's, GT1 Aston and McLaren are AFAIK basically out of meta more often than not, as these cars were not built to be competing with modern GT3 cars, and as such end up with a balancing headache. GR.1 is a extreme example of this, as you have non-hybrid older LMP1's, Hybrid LMP1's, Fantasy VGT's, a Hypercar, and Group C race cars all in one class.
And then you look at the oddball cars that dotted the earlier games and you have to ask yourself: Where would the old GT300's go? Into Group 4 where they would rot in a dark corner?, What about the old Cup cars?, if Polyphony were to add modern LMH/LMDH's, they would end up just being inferior to the existing LMP1s like the GR010 we already have. The current TS020 is the 1999 LMGTP version that on lap time should preform around the 787b, yet is not only in GR.2 rather than GR.1, but is woefully slow in that class. And don't get me started on what modern GT would do with the Tickford.....
Outside of contemporary GT3 cars, everything else would be popular while it is the flavor of the month, before people shift back to the meta. Hell even new GT4's and TCR's wouldn't add as much as people think while the AWD GR.4 machines continue to run the table.
It makes sense for Polyphony to avoid the hassle by limiting most new race cars to be introduced in GT8, when they can make a clean break from the current Group System, and in the process free themselves up to be more freeform with their future racing car choices, without worrying about their flashy new race car fading into the background due to the Sisyphean task that is balancing the current format.