I largely agree with the above, but with one exception, I cant support IETs▸ or derivatives thereof without any engines. A single engine is in my view a requirement for when the wires come down, so as to provide hotel power for some hours, or to proceed a much reduced speed to the next major station. As fitted to the nominally electric IETs used elsewhere.
Providing hotel power if the power supply fails does seem like a sensible idea, but I'm less keen on the idea of burning diesel to do it and I'm not convinced the 'self-rescue' capability is worthwhile.
My understanding is that the only "nominally electric" trains used elsewhere which have diesel engines are the
LNER» class 801s delivered through the Intercity Express Programme. Nobody else has thought it necessary to increase maintainance requirements and weight by installing diesel engines 'just in case'. I think that either the electric IETs ordered by Lumo or the ones ordered by Avanti West Coast have batteries to provide hotel power in the event of trouble. This seems sensible and I assume is a significantly lower maintainance option than a diesel engine. I'm less sure about the weight difference, but although the batteries might not be sufficient to move the train I would expect the likelyhood of this with an 801 is quite slim anyway since there is probably a pure electric train (such as a class 700 in the case of the southern end of the East Coast Main Line) stuck ahead of you anyway.
