There will only be 1 path from Chester-Warrington-Manchester Airport so a business case will need to be proven that North Wales can provide more Airport passengers than Helsby, Frodsham, Runcorn and Earlestown.
Commuters are less likely to use public transport for this, though, given that the airport has excellent road access from the west and plenty of parking spaces, and the train is rather indirect.
The Earlestown and nlw stops won't get removed off arriva services because the lime st- Warrington bank quay service is supposed to be getting diverted to Manchester Victoria at some point. Can't see merseytravel being happy with any loss of stops even if the service was doubled.
Merseytravel will adjust to the poorer access between the line through Rainhill and the WCML, I'm sure. There's not a huge amount the operator of a Chester-Manchester train can do to mitigate it given that the Northern and Arriva services currrently only overlap between Earlestown and Warrington, and Earlestown has an 8 minute minimum connection time to discourage anyone from using Arriva for one stop.
Newton-le-Willows-Manchester is certainly an important flow, but there are supposed to be extra trains for that.
Incidentally, I notice that Northern has an early morning
ECS move from Victoria to Chester on Saturdays, timed at 47 minutes for a Sprinter. It uses the fast lines through Warrington, which helps, but I don't know how much scope there is for Chester trains to use these (and so be more exposed to unreliability in the Virgin services), or to speed up the slow lines enough to mitigate the delay from using them. It gives some indication of the scale of the challenge, anyway.