And those traveling from either LGW or LHR or even I hate to say LTN would probably use an equivalent route from Southampton if they were available including myself.
The potential at SOU is huge but it's not being exploited enough and for the destinations I had mentioned earlier the aircraft wouldn't need to be any bigger than the current aircraft operating from the airport so a starter strip wouldn't necessarily be needed although obviously having that strip would be a huge long term advantage for the airport.