EasyJet I feel are the only ones (a LCC) who SOU maybe wooing, and courting - They have the correct aircraft for SOU ops, and the infrastructure.
If SOU can show them some grunt that their operation cannot be beaten, then EZY would have a business case to consider.
Whether EZY then choose to come here is up to them.
FR and JET 2 - no, cannot see it in the near term.
Flybe - ? Well, god forbid they restructure, or get taken over, then SOU without anyone else will be a dead duck.