I have no idea what I would call it. But i'd like.
1. Quality realistic physics - So I can drive it like a real car, working clutch etc. Plenty of games/sims already bring this, just not the ones who provide similar gameplay experiences (like Forza Horizon/Test Drive Unlimited)
2. Good presentation - Graphics/Sounds etc, not asking for miracles but just quality, plenty of games doing this already too.
3. Free to roam world to drive around in, taking it to the extreme I could use Lee Knights idea, plot a trip to the Nurburgring from my house and drive there, then take a lap around the track.
4. A home garage feature, similar to Test Drive Unlimited 2, only this garage is a real greese monkeys garage, I can modify and tune my car just like in the real world, I want to put a 2.2L VTEC into a Civic. Some games already bring this to some degree, though it could be done with more detail, accuracy and freedom.
5. Test Drive Unlimited 2 brought social features and the ability to drive free roaming with friends and view their car collections at their home garage, this was cool though it was an idea that really wasn't taken far enough, being able to have a meetup of 30 guys at their ingame house in a real scale sized world so that you can take a road trip together would be amazing.
6. Ultimately it would need a quality and large list of available cars/vehicles and tracks and the ability for the game to also be a traditonal track racing game with a possible ladder to climb in a racing career.
The game would be far too complex and large to realistically exist within the next few years but that is what I would like in a game. Essencially it's something that for the most part I already have in the real world. Problem with the real world is the price on supercars, insurance, tax, fuel and maintainence costs, not to mention speed limits and the law in general. If all these things were free and without issue then we would all be driving Ferrari's around europe at 100mph, rather than playing games.