It's certainly the route that holds most water as its the option that is likely to further grow the service as you say, frequency grows it not longer trains that may always be delayed.The ideal would be a second service per hour, but it may be difficult to path and would obviously cost more as you need another crew. And that might make the service so popular that you need 12 cars on both!
At least the Liverpool-New St is going back to 2tph, so clearly LNWR routes are showing good passenger numbers
== Doublepost prevention - post automatically merged: ==
Apart from Parkway, Winsford and Smethwick Galton Bridge, sure!but it seems to work fine on the 8-car trains at the 4-car stations between liverpool and Brum...
Smethwick is the worst culprit for UDS stations in both directions