If PD choose to go back to their roots and make a single player game with an adjustable level of challenge (GT3) and at least a couple different choices in career path (FIA GT series, NASCAR, Drag racing, Formula Drift/D1gp, F1, and LMP) it would make a good game. Correct the physics issues, and abandon the non-premium cars, and add some sort od penalty for bad driving (realistic damage modeling), and rewards for good driving (clean sector bonuses, clean race bonuses, sponsor challenges/parts, etc.) They would make the best racing game to ever hit any platform.
EDIT: Competitive racing does not a simulator make. Physics and other behind the scenes mechanics, the approach they take to making the chassis, tires, pavement, etc. all work together to give an accurate representation of a car. That is what makes a "simulator." One thing we cannot get from the current generation of racing games/simulators is a level of immersion that strikes fear into your heart when you over accelerate a corner, and genuinely fear for your life. Occulus Rift and Project Morpheus will be a step in the right direction. Without fear, there is no respect. Without respect, there is chaos and degredation.
P.S: when GT1 came out in 1997, there was no competition in sim racing. Just some food for thought.