The Avanti Voyagers/805s also work the Shrewsbury service (and possibly one of the Blackpools), which is a complication.
805s will also be serviced by Alstom/Hitachi at Oxley - another complication.
There is a Birmingham-Crewe-Holyhead service in the present mix, partly for fleet maintenance reasons.
Handing the service group to TfW would also put another TOC at Euston, not just VT/LM/LO/CS.
Chester/North Wales is not due to be serviced by HS2, so we can expect Avanti to show even less interest in it after that.
I suspect under TfW there would be fewer trains on the coast overall, as some services are near-duplicates at the moment.
No need for a 5-car MK4/197 when there is a 5-car 805 just behind...
I expect Avanti planned to use 805s like they used 221s in the past, for times when the wires are off on the WCML.
Would TfW fancy learning Stafford-Euston (they already know Crewe-Stafford) with all its alternative routes, and running at 125mph on electric (it's a diesel TOC at the moment)?
Also driver open/close, full restaurant/shop, running peak services at WCML places like Stafford and Rugby, doubling up at Crewe etc, etc.
I don't know how BR crewed the through services in the past (latterly HSTs), but in the distant past there were non-stop Euston-Chester services on the Irish Mail trains.
Although it seems a bit hairbrained, it is one way of penalising Avanti for poor service.
Though TfW is not perfect either.
Being run from Cardiff won't help: many Welsh folk, and WG itself, are inclined to think of TfW as "their" TOC and shouldn't be running "English" services.
There are/were clauses in the TfW franchise agreement about operating "English" services, and these would need a major expansion.
There's also WMT or whatever the West Midlands franchise turns into, who equally could also run 805s to Shrewsbury/Chester/North Wales.
I guess all this is speculation.