You'd hope this will tie into the GWR/Chiltern/Northern BEMU order to try get a consistent product, cheaper costs and ultimately down the line better cascade options.
Yes would hope for a big 10-12 year framework order, use what is available (and is reliable) in Europe and transplant it into UK size trains. Make it universal as possible (like the old C1 restriction mk1) rather than approved on a line specific basis.
I know it doesn't quite work like that these days and have to test it on all lines, but there is no reason not to check it on every possible route and diversion. As not likely to be used in South East could probably be longer vehicles nearer C3 restriction. Perhaps even standardise on minimum 150m platforms on regional routes.
I am in two minds about 2 different body shells, with same bogies and equipment (much like 444 & 450). It is certainly true a 5 or 6 car regional BEMU (with seating for 3+ hour journeys) is needed, but so is a 3or 4 car local stopper. I think trying to compromise on one design to fit both roles might give worst of both
Northern intends that their Class 781s will have a top speed of 100mph and be capable of lengthening to 5 x ~24m units, as well as ASDO and APCO capability.
Having read the specs of a number of recent European BEMUs, it is worth highlighting most have two top speeds, example 160km/h (99mph) on electrified routes, but 120km/h (75mph) on battery.
Clearly that 75mph limit on battery could be a problem on some routes. But presumably would need loads of extra batteries and/or really kill the range to try and exceed it. Not clear if Northern daftly hopes same performance on both mains and battery as comments only mention one number.
I have often thought a national BEMU strategy really needs about 100-200 miles extra electrified, some bays that are not yet wired, or in some cases more like wiring a long siding fed from one end to enable mains electric to clear a junction, accelerate away then drop pantograph. Also don't want to be doing changeovers on a busy main line when you got stopped just before a junction waiting for it to clear. In practice probably means wires for 300m approaching a junction signal, and nearer a mile leaving an electrified line if have to accelerate away from speed restriction at the junction. I am not sure the UK railway has really learnt how to use BEMUs effectively yet (so far they have only really been used on lowish speed stopping trains).
As for East-West, a suburban/local configuration what might do for phase 1, but really need those regional versions if talk of extensions beyond Oxford and Cambridge ever happens (to Bury St Edmond's, Norwich, Bristol via Chippenham etc). And of course they are multiple other regional lines that need 3+hour seating BEMUs of 5-6cars. In some ways it is highest priority with 156, 158, 159, 166, 168 etc needing replacing in next 4-10 years.