Honestly, a modern NR2003. I know iRacing exists, but it ain't quite the same, and the Heat games are not even close. Having all cars, tracks, and everything working out of the gate, with the ability to tinker and adjust to make it fit your preferences, incredible AI(Which could be done even better with modern tech)
No game since has truly allowed me to run a full schedule from Daytona to Homestead in a season long AI points battle.
I also enjoy the painting aspect, filling in the gaps: the backmarkers and special schemes, and adjusting the AI ratings to perform how I want.
Aside from that, I also would like to see a true successor to the ratbag dirt racing games, or a 80's IMSA GTP/WSCC Group C game.
Also SuperGT would be cool as well