What I'd like is this:
Complex string, possibly renamed to something like 'Gran Turismo Development course', coupled with an onsite 'wind tunnel' and tuning garage. So, you take in your car, develop it with parts, body kits, spoilers, tyres, suspension, drivetrain and engine upgrades etc, then go into the wind tunnel to tune your aero-parts, manage the air under the car etc, and then... onto the 'string' to put it through its paces. But....
The Complex string should be the 'infield', with the test course (the huge Nardo style high speed curcuit from GT4) around the outside to test speed and stability. Then, we should have a 'wet' handling curcuit attached to it aswell, plus an off road rally section...
You'll be wanting Millbrook proving ground then 👍