We've had this argument a few times already but... the planned numbers should mean half the services can run with doubled up sets (assuming that there's a half hourly Sheffield service and a half hourly Nottingham service)... and that's allowing 10% or so for maintenance etc... so plenty of scope for services that take advantage of the full length of St Pancras platforms whilst also being able to provide shorter services at other times (with the *shortest* services still providing roughly equivalent capacity to a seven coach 222, which is what the *longest* Sheffield trains currently get).
Providing anything longer than 5x24m means no scope for doubling up - and I'd rather we had ten coaches when most needed with five at quieter times than tried running a uniform seven coaches on every service. Keep it simple with one length of train, sure, but the capability to run doubled up services where needed. We don't want the complication that we have right now with five types of high speed stock (four coach 222, five coach 222, six coach HST, seven coach 222, eight coach HST)!
And having one fleet of 33x5x24m bi-mode 125mph stock should be easier for future cascades (rather than building something bespoke, given the problems we've had with trains like 460s before). The 804 might be something suitable for other TOCs to order too.
I don't think the timetable needs to be particularly complicated - no need for much joining/splitting - just simpler half hourly services (instead of the gaps caused by a combination of fast/slows).
Most importantly though (!), I'm glad that we are seeing 800, 801, 802, 803 and 804, rather than the nonsense of each new type of train being five or ten higher than the TOPS allocation of the previous type - finally, sensible numbers rather than the vanity of having a nice round number!