VS have had their bars on-board now for a number of years, and given the volume of pax flown, have had very few problems. The key factor, as has been alluded to, is that CC must remain in attendance and this is the model for VS.
The main issue here is that the CC MUST be willing and able to refuse alcohol, even to a full revenue pax/gold card/celeb/whoever. It's when this authority is not exercised that problems can occur (Vinnie Jones, Courtney Love, etc.)