Regarding connections to VS long haul, another complicating factor that VS long haul departures are spread right across the day so to offer competitive short-haul connections you need a good level of frequency on every feeder route, which could bleed millions in cash.
Virgin also does not have deep pockets. They rarely stump up much of their own cash. Any deal will be financed by someone else, and that won't be SQ.
Virgin may find a willing financier, but in the absence of any guaranteed financial return or brand recognition, I can't see what would be in it for them.