Thomas Cook and TUI Airlines both have flights to Orlando (MCO & SFB respectively), Don't think there is enough demand for a VS service to Orlando given than MT and TOM are only operating these in high season.
TUI have weekly flights to Cancun and Montego Bay, MT operate LAS and CUN in high season. I would think that they would be the most likely to bolster long haul at Stansted before VS would operate from a third London airport.