Having done a little detective work, I think this is a classic example of politicians not understanding what they were being presented with when the consultation was initiated. There seems to be a lot of crossness that the infrastructure won’t be fit for the services they want. There were never any proposals in the consultation to resolve the infrastructure on the Castlefield corridor, the proposal was always to deliver a reliable service on the existing infrastructure. So they can’t argue about that with integrity.
Andy Burnham also chooses his words carefully. The non-deliverability is almost certainly about timescales for May 22, given the scale of the service changes proposed. There would be lots of driver training to do, and potentially more crew required and more rolling stock (if the new timetable uses these resources less efficiently to create more recovery in the system). That’s not doable for May next year.
As @Ianno87 rightly points out, there will be deliverable options, but they mean that’s somebody loses out. Isn’t that what we elect politicians to do? Take the tough calls for the benefit of society as a whole?
It does strike me that the ambition of the proposals did not match the assumptions of the politicians.