Flybe
Flybe need to expand a bit further afield from SOU rather then saturate there French portfolio, maybe try a Lyon or Marseille route but I am surprised they have not ventured into Italy with the likes of Milan, Bergamo, Turin, Venice, Pisa, Florence also further into Germany with Berlin, Hamburg, Munich and also Copenhagen, Madrid, Vienna and Zurich.
I am not saying they should fly to all of these destiantions but they are in reach of SOU and important business and leisure destainations.
Maybe Lufthansa flying to Frankfurt twice daily with a morning and early evening flight and with a mid day Munich flight they seem to be expanding in the UK regions, also an Air Nostrum (Iberia) flight to Madrid perhaps 3 times a week would work.
I work in the cruise industry in the Port of Southampton and a large amount of German guests come to the port to join their ships especially from the Hamburg area, sometimes upto 500 at a time and many fly via LHR or even coach over so I honestly think a Hamburg service would be viable even if it was a summer only route.
Same with Madrid and and the amount of language students that come from Spain and in particulary Madrid to the Southampton/Bournemouth areas, I know they would not exactly make the route viable but with inward and outward tourism as well as business travellers I could see this route work well with flights 2 or 3 times a week.
Same again with Zurich, with Zurish Insurance having their UK HQ being based in Portsmouth, I know this route was previously flown by BA but SOU is a different place now and this is another route I think would work.
Perhaps Easyjet might move there winter only flight from BOH to GVA to SOU they may even expand to further routes if they did and make it a year around operation, I can't see there being any operational performance problems with their A319s from SOU and if not why the case for them to be flying from BOH when surely SOU would be more of an advantage to them as it has a larger cathcment area along with better transport options.
BAA should be looking at expanding apron space and extending the taxiways at SOU.