Given that travel to London from most places served by Avanti would be faster via HS2 (changing at Crewe for those destinations which won't have through HS2 services), I would focus the classic WCML more on traffic to and from Birmingham. For example, currently Liverpool-Birmingham has a semi-fast service at best. Meanwhile, Chester (and the north Wales coast) to/from Birmingham requires a change at Crewe or use of TfW's indirect service via Wrexham.
There should be fast Birmingham-Stafford-Crewe-Chester-North Wales services and faster Birmingham-Liverpool services. These could either be extensions of Euston-Birmingham Pendolino/80x services or possibly XC services? Either way, the main route for Chester-Birmingham through trains should be via Crewe and Stafford and Birmingham-Wrexham-Chester services should, in my view, either terminate in Chester or the bay platforms at Wrexham General (in the latter case, Wrexham-Chester would be supplemented by new services from Oswestry and/or Cardiff to make up the shortfall).
While I feel the current frequency of 3tph between Wolverhampton and Shrewsbury is an acceptable minimum, I would change the stopping pattern. Ideally, I think it should be:
- WMR clockface BHM-SHR service every 30 mins calling at Smethwick Galton Bridge, Sandwell and Dudley, Wolverhampton then all stations to Shrewsbury and
- TfW hourly clockface fast service, also extending into Birmingham but calling only at Wolverhampton and Telford Central on route to Shrewsbury (ie. no more Smethwick/Sandwell and Wellington stops)
This assumes the TfW service would use new heirs of class 158s/442s/444s that are fit for 21st century (ie. equipped with pantographs). If however TfW remain wedded to the likes of class 197s well beyond 2035 I would give that hourly fast path to whoever runs the WCML InterCity service by that point and have the TfW services from the Cambrian and Wrexham terminate at Shrewsbury. Either way, that clears the way for electrification between Wolverhampton and Shrewsbury.
Might need HS2 to be extended to Crewe to allow some of this of course.