Thanks for those replies. I wonder if it is possible to transport the hydrogen safely and economically from a railhead close to the chemical works to nearby depots by specially manufactured hydrogen holders on wheels. If this could be done at night with a revolving supply, I wonder what proportion of the northern fleet could become 321 bi-mode. The same applies to Teeside.
Maybe you could get to a position where it is possible to swap out all remaining 150x other than Yorkshire for hydrogen 321 Renatus. Maybe there is even enough for Yorkshire, but if not - maybe you go for 321 diesel or diesel battery there for now. There are a few stretches of overhead wire on 15x routes that might be interesting for battery re-charging so as to minimise diesel use.
Imagine a world where Northern gets to swap all its older diesel trains for newer and units that, to my mind, really do feel like nearly new after the Renatus refurbishment. Suddenly passengers are travelling on trains that rarely use diesel, have 4 cars, decent enough seats, climate control and the maintenance staff can start to work with a fleet of similar vehicles. As an added bonus the solutions have been put together by engineers in UK plants, hopefully building a body of knowledge in the UK that can be further grown to create some new UK ventures that can do that exporting thing we have forgotten how to do. The million dollar question is what the bill for all this would look like (on a whole life basis) compared to 15x business as usual.
If there are enough, I would personally like to see all the 319's replaced with Renatus as well but obviously there are contractual matters to consider there.
I for one am really interested to see how this plays out.