Can't really see 350s being fitted with galleys and catering facilities. So the 350s would not really require a Service Manager, First Class Host as well as a Train Manager.
No XC service centre at MAN so you can't do a TPE style of "bring your own trolley" via a ramp on the train.
How about 1 voyager per hour to MAN and 1 voyager per hour to Liverpool all operated by XC then LNWR provide 1 350 per hour to MAN and 1 350 per hour to Liverpool.
That would not allow any Voyagers to be internally cascaded to boost overcrowded services. Although if the Manchester LM service used double 350s it would resolve capacity issues between Manchester and Birmingham.
An 8 car refitted 350 could easily accommodate a trolley and a complementary first class offering be it just a hot drink and cake or whatever.
I understand that standards should not deteriorate but the exact reasons why Birmingham to Manchester would need a far superior standard to Birmingham to Liverpool if the Southern end was split off I don't know?
The spare 350s all have 3+2 seating therefore would need a full internal refit. I would match the setup of the Voyagers by having 1 dedicated first class coach per 4 coach unit.
My reasons:
1. We don't have enough stock to meet current XC demand (need trains capable of meeting current Voyager paths - with their fast acceleration etc - hence the of-discussed idea of eight coach HSTs being a non-starter)
2. We look like we are going to have a surplus of 110mph-capable DMUs (350s, 360s and/or 379s) due to brand new stock in the south east
3. We currently need seven (?) Voyagers to run the half hourly Birmingham - Manchester service
4. Liverpool - Birmingham is run by 350s every half hour
5. Something similar to the 350s has been used on services between Liverpool/ Manchester/ Leeds/ York for a number of years now
6. New Street has a terrible problem with air pollution
7. You could run an eight coach EMU on services from Birmingham to Liverpool and Manchester - with 2+2 seats - that'd free up a number of Voyagers (which are required on the remaining bits of the XC "core") and give Liverpool/ Manchester passengers a better chance of a seat (as well as soaking up more of the Wolverhampton traffic than a Voyager currently can)
8. Controversial idea, but how about giving the WCML franchise the responsibility for Birmingham to Liverpool and Manchester and giving the Birmingham - Oxford - Reading - Southampton - Bournemouth service to GWR (i.e. allowing XC to concentrate on the North East - South West corridor)? That'd mean giving GWR around a dozen Voyagers (puts down his crayon)
Downsides:
1. Platform capacity at New Street. No getting away from it (and I'm not naively hoping that punting everything along the line to terminate at International will be a "magic bullet" to get round things). Interworking the Liverpool and Manchester services at New Street may improve things, but I accept that infrastructure may be the sticking point
2. Through trains from Manchester to Bristol etc. For a while under VTXC there were no services from Manchester to the West Country (there was 3tp2h to the South West from the Yorkshire corridor and a bi-hourly service to the South West from Scotland down the WCML avoiding Manchester). Are the number of people doing through journeys of hundreds of miles worth inconveniencing passengers on the Manchester - Stoke - Wolves - Birmingham corridor?
3. First Class wouldn't be as nice on an EMU like a 350. Maybe not - though I'm guessing a Voyager isn't exactly amazing in FC? But, again, needs of the many and all that. But with modern eight coach EMUs available, you could tart them up quite nicely. There's only around five intermediate stops from Birmingham to Manchester (e.g. Wolves, Stafford, Stoke, Macclesfield, Stockport), so not like the First Class passengers will be inconvenienced by doors opening every five minutes (since I appreciate that some people get quite sniffy about having their journey disrupted by doors opening).
I'm not saying it's perfect, just that it's better than the status-quo (whilst we wait for HS2 to finally arrive).
Good post, there isn't a great interim solution, all have trade offs but the status quo should not continue for another 4-5 years.