Worth considering some trimming of the network.
For example, if TPE ordered one more 802 from the never-ending Hitatchi production line then they could provide a bi-hourly extension of their ECML service to Glasgow Central (thus a bi-hourly train from Glasgow/ Edinburgh to Newcastle/ York/ Leeds), which could replace seven Voyagers north of Leeds - i.e. terminate the current Plymouth - Birmingham - Glasgow at Leeds, extend some of the Reading - Birmingham - Newcastle services to Edinburgh - that would still free up a lot of Voyagers to beef up services through Birmingham.
As I've suggested before, we could replace a lot of Birmingham - Manchester services with EMUs to free up more Voyagers elsewhere - not *every* service but if you treat it as a four hour round trip then you could have a four-hourly Manchester - Bournemouth (hourly from Birmingham to Bournemouth) and a four-hourly Manchester - Bristol (hourly from Birmingham to Bristol) to maintain some through trains per day but permitting the majority of services on the half hourly Birmingham - Manchester corridor to be eight/ten coaches long. It'd mean some alterations at New Street, but given that XC already occupy a platform with their "hot spare", you could rejig things a bit. I'm not saying it'd be easy but this is a Forum where people like to suggest eight coach HSTs without accessibility modifications in the path of the current Voyager diagrams, so I'm not the only one.
Use the Voyagers spared from the above ideas to double up more/most Voyagers on the main Reading/Bristol - Birmingham - Leeds/York/ Manchester sections.
We don't have to maintain all of these long distance hourly services- we would benefit a lot more people by focussing resources on the busiest sections (e.g. by removing the Glasgow/ Edinburgh/ Newcastle/ York passengers from the current XC Leeds services, you'd free up a lot of space - and move those passengers onto the quieter Doncaster services).
The regional CC routes using Turbostars are just as overcrowded, cascaded Voyagers would seem overkill on these routes with their weight and wasted space at the ends for 125mph running.
Agreed - 125mph trains with large "crumple zones" inaccessible to passengers (that are going to be quite heavy for running through Ely etc) are not the answer to the current XC Turbostar routes (esp given that a four car Voyager isn't going to be much of a boost compared to a three coach 170).