In Spring next year, Avanti are planning on introducing 13 class 805 - 5 car units to be doing both North Wales and Shrewsbury lines according to the British_Rail_Class_805 page
https://en.wikipedia.org/wiki/British_Rail_Class_805.
Now since the class 805 are EDMU units, I am suspecting that they would be working electric to Crewe from London Euston and then diesel to Holyhead/Shrewsbury, otherwise why lease these trains?
There is also going to be similar 10 7 car class 807 units, but with these just being electric units to do Blackpool North and Liverpool Lime Street from Euston. This will enable the 18 class 221's to be withdrawn.
Now, I personally believe that the Avanti Crew to Holyhead service if paths available should be extended to Birmingham International. This perhaps could happen once HS2 - stage 2 is built, but with the service still using the classic lines so that the service can be stopping at Stafford and Wolverhampton. The more direct service from Holyhead to London Euston should then be using HS2. I know that there is a Transport for Wales Rail service to Birmingham International, but this goes via Birmingham New Street, Smethwick Galton Bridge, Wolverhampton, then via Telford, Shrewsbury, Wrexham route to Chester rather than via Crewe, then Chester to North Wales which is the route that Avanti West Coast takes.
Now, I know some have said that there is not currently the numbers for these type of services. Are the numbers being used current numbers or numbers prior to Covid?
I would add that you certainly need trains that are timed to meet the ferries that have come over from Ireland and again, if not going to London Should be going via Crewe, Chester to Birmingham International.