Right now, all packs *should* be compatable, if not accurate or balanced. I think. So far as I know, that should continue to happen - although it is true that the game might require a change requiring a new version of the .girl or .rgirl files. If that happens, there's not a whole lot anyone can do about it except redo the old packs, which would be pretty easy, if time-consuming.
Randomizing all girls' stats at the beginning of a new game is an interesting idea, though... So far as I know, it should certainly be rather easily doable. As a selectable option, I could see it being implemented.