An A319 would be ok performance-wise from SOU - fairly similar to the E195's in fact but the way the stands are means it can only handle 2 at one time (three would be possible with re-marked stands) and JobsaGoodun is right about the distance between the stands and runway, tails have to the below 9m high on the East apron. Not sure if EZY would want to dilute some of their own Gatwick traffic too much though if Flybe did go belly up. Actually a little off-topic but it would be very interesting to see who would replace Flybe at SOU if such a thing did happen.