Great news for SOU. Being plugged into the EZY network coupled with their marketing and brand awareness should really put the airport on the map for those people who perhaps aren't aware of it at the moment, particularly towards London.
I hope we'll see more routes to come for next summer. Another advantage is that with EZY having so many bases across Europe and the UK flights could operate into SOU from many different potential locations without any aircraft having to be based.
I do wonder if this will hole Powdair below the waterline though (at least at SOU), or whether they'll benefit from the (hopefully) increased numbers of people looking at ski routes to Switzerland out of SOU? Their flights don't operate on the same days as EZY from what I can see.
I reckon we're now going to see some significant airside investment at SOU in order to cement EZY's position there over the next couple of years, and really expand the airport's appeal in order to start taking traffic from the two closest (pretty much full) London airports. Interesting times ahead.