As far as racing seats & roll cages are concerned, you'll probably never see those implemented until the GT series implements a damage system. I don't think they have because some of the manufacturers would raise Hell.
As far as the other interior and exterior stuff goes, that isn't GT's goal. They call the "the real driving simulator" not "the real Pep Boys simulator" (sorry, had to)
But they have had the Wheel Shop for a while, so ya never know what else might get thrown in.
And I think even in GT2 a drop in ride height was noticeable in game play.
