And to Hull, Harrogate, Lincoln, Sunderland, Middlesbrough, Huddersfield and when required around via Spalding, Askern, the Durham Coast, Tyne Valley, Castleford, Cambridge... Ends up being a fair few locos that!
True!
Plus the practicalities of finding space at a busy station like Waverley to attach a diesel locomotive...
...and the subsequent problems with joining/splitting trains (fine for a 5+5 80x to split so that the quieter extremes of a route can be served by a shorter train but what do you do if your ten coach train
plus "top and tail" power cars
plus the diesel loco dragging it are trying to find platforms long enough to accommodate it at intermediate stations at the "non-London" end...
...and the large number of additional carriages you'd need to build to maintain the same capacity at the London end (given that your five-coach portion for some "non-London" destinations now needs to be a ten coach train due to the inability to split...
...and the potential loss of capacity at the London end, given the room required for two power cars compared to the much smaller "crumple zones" on DMU/EMUs...
...it's a nice idea, don't get me wrong - I like the idea of the main ECML/GWML trains using the same carriages as the loco hauled TPE services, as this would make it a lot easier to order subsequent batches (e.g. XC/ MML or just capacity increases on the ECML/ GWML/ TPE) - that sounds preferable to having "bespoke" stock - it's a nice idea in theory but I think we made the right decision.
It'll be interesting to see how the people so quick to complain about the "utilitarian" décor of the 80xs and the "functional" seats (compared to beloved HSTs/ Mk3s) is replicated on the Mk5s and they realise that it's a "new train" problem rather than a reason to bash multiple units that replace "proper" trains with a loco at each end.