The problem holding back SOU development isn't simply the runway length. Due to a requirement to provide a minimum length RESA (runway end safety area) 73 metres is lost from the 20 TORA, resulting in only 1650 metres being available, less than SEN. Secondly there is a horrific tree problem off the south end of the runway together with the hill. These are performance (ie take-off weight) limiting. The hill cannot be moved, the trees can. Reduction of one group (ie believe called Marhill Copse) would significantly improve the situation and permit an increase in take-off weights/range.
The taxiway situation isn't simple. When the site was re-developed many items of the family silver were given away to secure quick planning consent. This included the punitive night flight restrictions and an undertaking not to build a northern taxiway that would take aircraft closer to houses in Southampton Road (Eastleigh) than they would be on the runway at its north end. Consequently, any extension will have to either be on the east side or stop short of the northern end of the runway (effectively ruled out due to building of another of the many car parks).
Thanks to BAA SOU is a catalogue of missed opportunities which will hold back long term development without multi-million pound investment, how deep are the new owner's pockets? Or is it just a case of eventually throwing in the towel and selling off the site for non-airport development when growth isn't worth the investment?