I think there's another element driving VS. As long as they have to put their passengers on BA domestics there is a commercial issue. BA will lift the ticket coupon at Manchester and that will give them visibility of the fare ladder routing etc. With their own flights they can keep that data in house. It also extends their reach for Upper Class because they will be able to offer limo service to a large tranche of the NW plus most of the populated bits of Scotland (even Glasgow).
I suspect that Hartington has it right plus the fact that any airline totally reliant on their major competitior for feed is accepting it is no longer in complete control of its destiny. Insofar as who will operate the service, there are a number of EU Ops 1 carriers with much lower crew costs than UK carriers which could provide the service at not a huge cost to VA.