Well EasyJet are more than welcome to base two Airbus 319s at Southampton especially as it seems the Flybe sun routes will more or less disappear for summer 2018.
If Flybe do discontinue the sun routes there are numerous destinations that Easyjet could potentially serve from SOU with no competition except to Ibiza and Palma and those two are only served by Volotea 1 and 4 times weekly respectively and seasonal only.
With two based aircraft at SOU potential routes could be to
Alicante, Barcelona, Berlin, Faro, Geneva, Malaga, Milan. Nice, Prague, Venice.
Obviously just wishful thinking on my part but I honestly think that EasyJet could do quite well out of SOU in a 'similar' way as they have done at Southend.