If anything, I would lean towards simplifying the eligibility criteria to:
a) receipt of PIP and equivalents in devolved nations,
b) eligibility for disabled persons ENCTS and equivalents
c) those ineligible for a driver's licence due to a medical condition.
I think the difficulty that the railway faces is that it can't just go off PIP anymore, because of the way that the eligibility criteria for PIP have been changed. The PIP descriptors for mental ill-health, neurodivergence, and intellectual disabilities are very tight, restricting the benefit to people who cannot follow a common route. By design, the descriptors exclude a lot of people who would need help for unfamiliar or long-distance journeys. Even the PIP descriptors for physical disabilities are tightened- if you can use prosthetic legs, you probably won't be eligible for PIP.
It's worth noting that (c) in your list is a qualifying criterion for an ENCTS pass.
It's also worth noting that mental ill-health and neurodivergence do not qualify someone for an ENCTS pass either, unless their issues mean they would be denied a driving licence. The requirement is to have a learning disability which must have started in childhood. This also means that having a long-term brain injury or a degenerative brain condition wouldn't qualify you either (although, in practical terms, someone with a long-term brain injury or condition would likely be eligible because they'd be unfit to drive).
This option is essentially just outsourcing the conditions list/eligibility validation to the local authorities
It is, but eligibility for ENCTS/Freedom Pass/etc is a qualifying criterion for the Disabled Person's Railcard from March 2026 and the local authorities are making the assessments anyway. There doesn't seem to be much point in RDG re-inventing the wheel.
It'll be interesting to see the wording of the eligibility for phase two in September 2026. I strongly suspect that it won't end up being as generous as it looks at first glance and that quite a restrictive view of
"a substantial impact on a person's ability to travel by train" will be taken. But I am just speculating.