Well lets face it, car modification has been on everyone's lips since GT2, and bringing in being able to racing modify 17 cars out of over 1000 just doesn't cut it, at least have racing mod options that let you choose between say 5 preset customization's, and on at LEAST a few hundred cars, because that is what IS losing people to the Forza franchise.
I have been a GT fan since the first one came out, and have stuck with it, but if number 6 just does what they did for 5 and copies across all the standard cars that were from number 4, and we have 800 outdated looking cars with no interior view, no customization, and physics that feel like they were taking from the megadrive, GT will continue losing its fans, until they are not selling enough to make another.
So customization, physics, NEW cars or at least old ones redone do that they look like they are pushing the PS3 barrier, are not things we want to see, they are things we need to see, to see the greatest racing franchise continue to thrive!