It must have worked up till fairly recently with the Crewe-based Mk3 set and its Crewe-Chester-Manchester-Holyhead-Manchester-Llandudno-Crewe diagram.
Why could that not be a Mk4 diagram in the future?
This also worked some summer Saturday services along the coast.
A couple of things have changed since then. Firstly, the entire diagram bar the first leg from Crewe to Chester to in the morning was worked by Llandudno Junction guards (and in the final timetable, they worked that bit too). Now, nobody at Junction signs MKIVs, nor are they ever likely to.
Secondly, with the extension to Manchester Airport (and the changes since Covid) the diagrams may well have changed and trying to keep it to a self contained diagram only worked by a limited pool of staff may be more complicated than it was before (and it was awkward enough to do last time around). And that's assuming Holyhead crews are available and not tied up with other things (like learning 197s).
It would also probably require getting the MKIVs cleared for Chester - Manchester which might not be straightforward or cheap.
Agree that it must be a phenomenal backlog, perhaps very slightly lessened by sending the 170s to EMR. I believe the plan was for 170s to work Central Wales and Salop-Crewe which must have involved Salop and maybe Crewe crew too. As it is everyone except Valleys needs to learn 197 which is presumably the core traction now.
I am guessing that whichever crews who are learning 67s for the first time also have to learn the art of loco driving too, which is somewhat different to driving a multiple unit, particularly in terms of braking. Is it TfW drivers who do the coupling and uncoupling of 67s to Mk4s ? Or do TfW have that rare breed of orangeman ?
I've not done the MKIV course yet so can't speak for it, but I know of the old three week MKIII the vast majority of time was spent learning about the loco itself. It's certainly a big change for drivers who've only ever driven units!