It used to be the case when I first received DLA numbers of years ago that the Local Authority where I lived had a ‘voluntary list’ which people were encouraged to join as it was useful for them to attract funding for disability provision in the area.
On the idea of the ID card itself I’d prefer to see an ID card that was multi-purpose so could act as an accepted photographic proof of ID/Address for those of us unable to drive and it could also be ‘loaded’ with information including any ‘entitlements’ (free bus pass, exemption from tolls, reduced charges etc).
At the moment, if one is unable to have a driving licence the only other ‘acceptable’ proof of ID is a passport but having to carry it around all the time isn’t very secure. When there was a proposal for a voluntary ID card a number of years ago I was very keen but it didn’t happen.