Besides, I believe the Newcastle-Man Airport train will be readjusted to go to Liverpool instead in the near future.
Err? I doubt it. I understand Manchester Airport shelled out heavily to get the train operators to terminate at the Airport instead of in town, for the very reason that station departure screens across Northern England would feature Manchester Airport as a destination, most particularly in places like Leeds, Liverpool, Newcastle, Darlington and Carlisle - places with their own airports but no overground rail link to speak of.
And who'd want to go to Liverpool? If the Newcastle-M'cr Airport service ceased, folks would have to change trains at Manchester Piccadilly, making a direct air service twice as attractive.
I agree that such a service is unlikely; but as another poster had mentioned it, I reminisced how nice it would be to have something like the old Dan-Air Link City service - though at a frequency that made sense. Plenty of people fly Manchester-Edinburgh, so those aiming for the Berwick corridor may prefer a Newcastle service.