There is a substantial amount of traffic from this line, particularly Orrell and Pem in the Manchester direction, from my experience over two thirds of traffic in this area is through traffic at Wigan so terminating at Wallgate is a non starter.
I know. I commute to and from Pemberton when I can - but they key words there are 'when I can'. The service as it is now is woefully inadequate. Trains start too late, finish too early, are slow, dirty, too small, and too infrequent.
An all day, 15-min Merseyrail electric service which connected with the fast Wigan-Manc services in the town centre would be an overall huge reduction in journey time, and increase on the current 1tph for part of the day service.
More importantly, a 15 min electric service would allow Pemberton to become a park-and-ride off the soon to be built M58/A49 link road which would, if it were priced right and properly promoted, be a huge bonus for Wigan.