While we're talking about things we can never have, I'd like the option to switch to Assetto Corsa's physics model. I feel AC's steering feel, clutch and brake simulation are superior to GTS. It's not that GTS physics and FFB are terrible...it just feels like driving with a condom on compared to AC. If you've played both with a wheel, I think you'd know what I mean. And if Ferrari and Porsche employ Kunos Simulazioni (AC's developer) to develop their in-house simulators, they must be doing something right.
For me, the perfect game would be GTS visuals and Sport Mode + AC physics and FFB.