Apart from a master plan to extend the runway by only a small marginal amount (which is still going to be some years away) SOU will always be restricted with its operations and operators - the other issue is current lack of stands for bigger a/c.
The runway will never be extended in our lifetime to offer performance for larger and heavier aircraft to fly further - the location of it means it is simply impossible due to obstructions at both ends - Future money will be never available to move the M27 or the railway!