Who says they're actually going to operate this? The closing date for the applications to the trustee for the IAG slots (for ABZ and EDI) is... oh, there's a coincidence, the day after tomorrow (see
here). As
bad bear says, the Commitments (not the band, but the conditions linked to from the above page) stipulate that they can't be leasing out their own slots while applying for the IAG slots.
Plus, wouldn't it be helpful to VS's case to be able to say "we're really committed to making this UK domestic network work, Mr Trustee - look, we've even launched another route in anticipation. Please, give the slots to us, not those nasty Aer Lingus people, just because they have extensive short-haul experience, the right aircraft, and a presence in the relevant markets!"?
I think at this stage this is just window-dressing. If they get the ABZ and EDI slots, yes, they may operate MAN too. But if they don't get ABZ and EDI? I just don't see MAN taking off in isolation.