I don't agree that a full fleet of new, fixed formation 9 or 10 x 26m units for XC would be overkill, there is so much suppressed demand that I highly suspect such units would end up paying for themselves through all of the additional revenue - sadly there is no way of actually quantifying this without it actually happening though, so the DaFT won't do it.
The thing is to deliver a universal 7 coach fleet would require more coaches, and so would be the more expensive option, the whole point of the mixed 5/9 coach fleet was that it was a similar sized fleet in terms of coaches:
312 - current fleet
342 - current fleet plus the 6 in storage
304 - mixed 5/9 class 800 similar fleet (12×9 and 40x5)
332 - upgraded mixed 5/9 class 800 similar fleet (19×9 and 33x5)
364 - universal 7 coach class 800 similar fleet
Even with the 221's in storage (342 coaches) a universal 7 coach fleet (364 coaches) requires more coaches.
The upgraded 5/9 coach fleet could deliver (with 85% fleet occupancy) 16 of the 44 diagrams as 9 coach sets (roughly 1 in 3).
Yes they maybe carrying around a lot of fresh air, however if the lease cost is the same per coach (and bearing in mind a bimodal train would be cheaper to run and the staff costs, due to there being no second unit to have extra staff in, would also be lower) the cost is no higher than the current fleet plus the 6 units in storage if that gets sign-off.
Likewise, the cheapest Passenger Variable Usage for a class 220/221 is 20.23pmp, so 101.15pmp for a 5 coach unit whilst the class 800's (and they have lower charges for the full length units vs the short length units and differences between motor and trailer coaches) are 100.67ppm.
Such a small reducing may sound like splitting hairs, however with a sightly smaller number of coaches in the fleet there would be a measurable level of savings, especially once you start taking of millions of miles per year (each diagram wouldonly need to average 320 miles for the fleet to be doing 5 million miles and so even at that level of a difference of 0.48ppm is £24,000 a year) now whilst tiny in termsof the costs of the railway (£24,000 is likely 1/9th the cost of the lease of 1 coach) it's still a saving. Although it's worth noting that the 221's have a higher charge and so the savings are likely to be more than this.
It's also worth noting that a 9 coach set would cost 152.51ppm and so whilst higher than a 5 coach set, only by around 50% and so compared to running a 5+5 train the cost savings over that same 5 million miles distance would be:
£7,625,500 - 9 coach train
£10,067,000 - 5+5 coach train
At £2,441,500 in savings, if we assume that the lease costs are £200,000 per coach then that's 12 coaches of the fleet paid for.
Even if the actual milage for the 8 coach sets was 2.5 million miles that on its own could allow the new fleet to be 2% more expensive per coach and still cost less in lease charges than the current fleet.
Therefore, any extra passenger revenue would go to reducing the subsidy, and I suspect that there would be a reasonable number of extra passengers.
Worth remembering that the Voyagers are currently going through a refit. It would be highly inefficient to bin them for a new fleet straight after, and options for cascading are limited now Scotrail is taking the 222s.
Taking all spare 221s seems like a better compromise, preferably quickly before an open-access operator gets them.
Then make whatever timetable and staffing adjustments are necessary to ensure everything along the Manchester/Newcastle to Bristol/Reading core can run as doubled-up sets, with no units locked out of use. Units could then split/join as necessary for extensions beyond Newcastle/Reading/Bristol, and some extensions could be cut back to 1p2h (or less...) if needed to save diagrams.
It's not the ideal solution, but it's a reasonable compromise IMO.
It's likely to take a while for the new fleet to enter service, especially given the need to go out to tender, as such 2030 isn't an unreasonable timetable for the whole new fleet to be delivered (and the 22x's to go out of service).
However, the maths of the new fleet gets better if we've expanded the fleet with the 6 units in storage.
If lease costs are comparable per coach the in service fleet seat count could rise:
13,024 - current 22x fleet
14,331 - current 22x fleet + the spares
17,630 - original 5/9 coach option
19,528 - upgraded 5/9 coach option
Even between the two 5/9 coach options that's a 10% increase in capacity. I think that most people would take that as an upgrade.
However, even between the current fleet with the extra 6 units to the original 5/9 seat proposal the increase is 23%.
However, that increase in capacity could be delivered for a cost of no more than £0 in lease costs over the extra 6 units even with a 12.5% increase in lease costs per coach over the existing fleet.
Whist to be able to make the same "cost no more than £0" for the universal 7 coach fleet there would have to be a 6% reduction on the lease costs per coach (either in other savings and/or in the actual lease costs).
Whilst not entirely impossible it does make the 5/9 fleet the cheaper option whilst still delivering a decent uplift in capacity.
A 7 coach unit with 70 first class seats and 404 standard class seats (it's likely that first class would be 2/3rds of a coach rather than a full coach, both plus the end coach, so seating numbers might be a little higher) would be:
20,856 seats in service
Given the already significant increases in capacity between the existing fleet plus 6 units option and the original 5/9 mixed fleet (+23%) is a further 18% increase from the original 5/9 fleet and the universal 7 coach fleet likely to be justifiable?
Even if it might be, the extra 7.8% capacity over the upgraded 5/9 fleet option is likely to be too small to go that extra step for the extra cost.
As such whist the ideal would bethe universal fleet, I suspect that it's a bit of a step too far for the government to approve.