So far as I know, Platform 7 was, at one point, designed with passive provision for a Platform 8 in mind, but sadly it seems to have then been built simply so as not to preclude another platform being built, rather than being a definite template for its layout. I believe the chances of needing another Down Fast platform in the immediate future is probably fairly slim, provided nothing more than the half-hourly Gatwick Express and hourly ish North Downs trains remain the only ones which usually occupy platforms for any significant lengths of time.