This would be the pattern I would imagine, and agree Wilmslow is the outlier there - but a relief service might only have the paths to run Cardiff-Crewe (Crewe offers many more connections beyond Manchester - it would work out) - and so Wilmslow would be down a service. But I doubt there is much demand Wilmslow - west of Crewe in itself.
If the Liverpool plan came back, that would add frequency south of Shrewsbury too, of course - useful especially for Leominster, Ludlow and Aber who are on the busy side for mostly 1tph.
Thankfully, no one has actually decided to launch such a service.
Although I do not have the numbers, the impact on service to places like Abergavenny, Leominster and Ludlow would be terrible. You are inserting connections for what? The line does not need high top speed, so just gear for more stops.
Given that the Mk4 is considered "Premier" then the fact that 197s can do the same time but serving more communities tells you exactly what is needed. We do not need a premium service we need a service that serves more people and still keeps to the same time (i.e. trains geared and built to stop and accelerate more)
Anyone who wants trains that have long gaps like Newport to Hereford to Shrewsbury probably needs to go from Taunton to Reading as I do not think we have many in the South West that only stop once an hour. Certainly long spread stops is not what the Marches should be about.
I am not saying you in particular. But it amazes me that people look at the 09:53 and 10:53 departures from Cardiff and think the latter is a better stopping pattern for two trains that take exactly the same time. (For reference the "Premier" stock is so useless that today's 10:53 is a 197 as was the 06:46 which was also advertised as being reject ECML junk)
Is it worth investing in "Intercity" stock that has a lower maximum speed and is geared to accelerate and dwell for shorter times? I doubt it. It is also worth noting that the highest standard seating capacity train is the 5-car 197 and that is overkill for most services. So essentially you are building a train for a bespoke Intercity setting and only need a few of them.
More 197s would be absolutely fine. If they can be made to work part of the route on battery and charge between Crewe and Manchester, or Newport and Cardiff, then that would be an environmental bonus.