LTNman
I cannot really see SEN benefiting from any LON overflow for a couple of years at least and I think it will have to rely, as you infer, upon its attractiveness to travellers within its natural catchment. I tried to demonstrate that that market could prove attractive to another LoCo or, even as is being seriously suggested by some at SEN, to EZY again. I don't share that optimism myself but we live in strange times do we not?
I do remember being told from a reliable source that following the launch of the initial EZY routes the airline found the booking patterns more in line with a regional airport than a LON one. Maybe in 'normal' times SEN couldn't really hope to enjoy a sustainable market greater than that, despite all its efforts to reach beyond it. The size of that market is still considerable though.