Well before we reach a dozen flights per day it shoud be possible to fill 777 or 787 from somewhere like Brum or Manchester.
If only it were as simple as that.
BA has 9 LHR/MAN rotations per day, 11 on LHR/EDI, for example, all with A319/A320/A321.
Don't you think they would have tried doubling the aircraft size and halving the frequency if they thought that would work ?