The common travel area + Brit_card might result in an interesting pattern where ID is by association rather than territorial location. For instance, as nationalists reject it and use only IRE/EU equivalents where possible. The passport is somewhat similar already. Would people reject services and jobs in N.I.? Completely possible and it already happens with people working "down south" aka down the road.
The civil liberties concerns, particularly in N.I. (historically speaking), are also important to consider. There is quite a high capacity for discriminatory practices in the region from all angles.
On the other side. The British government are lowering themselves to the position of "just another app on my phone". A system riddled with viruses, cyber attacks, etc. Further, what is to stop groups simply setting up and alternative ID system running on btc or something in the future...if this becomes the norm? At first it would be useless and a farce. Later a complete separate system.
Anyway, horrible idea all round. They clearly have not thought this through. Paper ids and loose associations are things I am a fan of in the anglophone world.
