The A319 has immense takeoff performance, and could probably operate quite reliably out of Southampton to at least the south of Spain, Portugal, Italy and Greece, if not the Canaries and Cyprus.
I believe the A320neo also has rather impressive takeoff performance, but not quite to the same standard. If EZY ever get the Cseries... SOU (and a lot of other minor bases/operations) could be onto a real winner
I wish EZY and SOU the best and hope it turns into something good, SOU is one of my favourite UK airport. It was just, hands down, a lovely experience from start to finish