I was slightly confused as to why BA decided to launch all of those routes from LHR, as I find it is a waste of slots and all of these routes can operate successfully out of Gatwick, along with their array of leisure routes.
A certain trend of BA lately is to launch currently served routes from LHR at Gatwick, like Vienna and New York for example. This is why I was thinking routes like Paris, Berlin & Miami could be great for Gatwick. I was also thinking that BA could change their Milan operation so that flights to Milan Linate (for business & transfers) operate from LHR and flights to Milan Malpensa operate from LGW (for O&D traffic).
Other routes from BA that they could potentially operate in the future:
Montego Bay?
Phuket?
Dubai? (replace one of the LHR rotations with an LGW)
Havana?
San Francisco?