I can see two things I really want in the narrow car range with the fully filled out game around it.
1) Formula 1 - yes we have the Codemasters games but the FFB and the physics are quite bad even in 2020 and something more sim like would be really nice. But I think the entire career mode they are doing quite well. The interviews may be verge on the annoying end of things but its a nice idea and the MyTeam management is fantastic. They are getting the rulesets and such bang on, it really is just the driving that needs improving.
2) FIA world endurance championship - Having a "MyTeam" and all that lovely Codemasters style game around a simulation for modern endurance racing would just be fantastic. There is plenty of variety in the cars across the classes but its also narrower in its focus than most games that might have multiple class cars. Most games have done poorly for endurance racing for a variety of reasons and this could do well just by being multiplayer focussed but a great single-player experience (with shorter than 24-hour races with say simulated partners) could be interesting too.
Mainly I think the sims of today are missing the rulesets in races in terms of flags and penalties and such but also that out of race career mode or multiplayer career and finding of good races. That is the next stage in sim progression that needs to happen IMO.
To be honest....Im happy with IRacing, AC, ACC, RF2 and Automobilista2. A few years ago I wished that a Hillclimb Simulator would exist. But with the modability in AC, I dont need that anymore. I have the most presticous Hillclimb tracks around Europe in AC...mostly from Germany, Austria and Switzerland. So for me no new Sim wishes at the moment
touring cars, sort of evolution from 1950`s upto modern day
you progress through seasons starting 1950 and cars will be unlocked after every season just as in real life.
you could also do the same with sports car classes too,
Indy car without any doubt.
However I would prefer some past times, like '90es say but I would not complain if getting any. I love just throwing the indy car around in Long beach in Project cars 2 so... imagine my desperation
Classic Group C, that would be amazing!
For me it's the epitome of racing.
I'd bolster the sim with other classic groups. These cars exist and aren't keeping secrets. Every aspect could be recreated in minute detail.
You could make an awesome career experience!