I didn’t own GT6 so didn’t even know gauges where an option. But yeah, I’m trying to think of things that can be used on most models. Particularly road cars.I don't think GT Sport will ever feature visual upgrades like wings and splitters. Also, aftermarket steering wheels sound cool also but more realistically I think PD would bring back the aftermarket gauges from GT6. My guess would be that you could buy different gauges like a tach, temp, boost, etc. and in different colors from the Mileage Exchange.
At least for GT Sport, if they added aero parts, they would need to be generic ones we can use on all road cars. Can’t expect them to model specific aero kits for each car. Maybe for GT7.