It is hard to imagine Virgin switching to SFB as the extra volume of passengers would absolutely swamp that airport. The idea of three (extra) Jumbo-loads of passengers trying to fit into the departure lounge would be a nightmare. It would also be a huge retrograde step for their scheduled services, as the links out of SFB are very limited compared to MCO.
However, if it was a limited programme in peak season, that might make more sense, as it would operate on more of a charter basis, which SFB handles well.
It is a very interesting line of questioning, though, and indicates Virgin is possibly looking to cut costs once again. We await developments on this with great interest.
SFB is certainly a longer drive to most resorts than from MCO, but it can often be 30-45 minutes quicker to get through, so it is a swings and roundabouts deal. But, MCO is a much nicer airport to depart from as it has so many more facilities and SFB is not geared up for lengthy delays (which is obviously always possible with charter flights).