SOU might well work for connections with flybe, just as MAN seems to sustain a daily Q400 during the season
A few years ago (perhaps 2010?) BE loaded SOU-NQY flights, can't remember frequency as they were only bookable for a few weeks before being taken off sale. So they have looked before but for reasons unknown didn't start it. However I can see it working as long as flights are timed to make reasonable connections. Likewise the MAN link - I assume the timings are aimed at tourist/leisure traffic as opposed to giving the NQY catchment opportunity to make viable connections at MAN. Flights from places like NWI and SOU have been timed to make good connections with TCX long haul flights amongst others.