With all these suggestions of routes that could work from SOU,there is one major long term problem,and that is simply that the airport needs progressive,driven management,and it hasn't happened and unlikely too with the present management.
Take a look at Jersey airside and structure improvements recently announced, to see how to move on with airport improvements.
It's not happening at SOU and there is no short term possibility of it happening.I don't think there is any real prospects of route expansion with the existing set up at SOU