TrueBlue - I very much doubt Gatwick will become as successful as Heathrow, because of what is know as the 'network effect'. Virtually every airline at Heathrow will accept connecting passengers from a sizeable proportion of other airlines. The largest carrier at Gatwick, namely Easyjet, along with a number of other Gatwick based airlines, does not accept connecting passengers, and thus the benefit of the wide range of desitinations in the network is significantly diminished.
Until the acceptance of connecting passengers at Gatwick increases significantly, it will remain an O&D airport, instead of a hub like Heathrow.