You do realize that PD is working on it now, I almost gaurantee it. It's the best time to do it if you think about it. They have up to date data on some 740 cars, all the photos taken for each track(around 35,000 pics per track) and car (around 700 pics from every concievable angle for each car). They will most likely use the same phisics engine because it has been in developement for years and is outputting realistic test results. (I heard some manufacturers did tests on concepts in reality and w/ the GT4 physics engine and got very similiar reasults) Why throw all that work out. For GT5, all they need to do is improve graphics(which is mind boggling in itself, as they're so good now), add tracks and cars, and maybe some more features, like customization/Race modification, etc.