If the line from Chester to Holyhead were to be electrified, then what service would you run on it? Manchester - Llandudno would stay the same (with EMUs replacing DMUs), but what about the two bi-hourly Holyhead routes?
- Holyhead - Llandudno Junction - Chester - Wrexham - Shrewsbury - Wolverhampton - Birmingham - Birmingham International
- Holyhead - Llandudno Junction - Chester - Wrexham - Shrewsbury - Newport - Cardiff
The benefits of electrification seem wasted if you are going to have half the units on the line west of Chester run by DMUs still. Terminate them both at Chester and replace with a Holyhead - Chester - Crewe - London service? But then you'd lose the "political" WAG Express...
A think a teeny bit of running under the wires would be fine, so the WAGs would almost certainly continue as is. Maintaining
some kind of service to Cardiff whatever happens.
IF they wired to Holyhead, I would hope that by that point they would have already done Wolves-Shrews. So throw in the extra via Wrexham, and you have your Birmingham International.
If however, Labour WAG woke up tomorrow and said "I know, lets electrify Chester to Holyhead (with DfT finishing to Crewe)", then I expect that diverting the normal bi-hourly services to Crewe would be the best move.
Any kind of electrification in Wales would be like this (apart from the Valleys), which probably explains why none has been done yet. Once they start, there is massive incentive to do as much as possible.
It obviously won't happen for a while (I would say 20 years at the least - BHM to Newport will probably go first), but it will eventually be very interesting to see what happens...