I don't see it having much impact on immigration but I don't have a problem with a digital ID card. It seems to work well in some European countries that have it. Estonia in particular seem to have nailed it from what I have read.
Why carry a driving license, passport, NI card, proof of address, whatever, if you can have it all centralised on your phone?
I don't think it's going to be very popular, and the weirdos who cry about a cashless society will have a big problem with it, but there's plenty of reasons to do it.
Feels like it would be something like the smoking ban where loads of people kick off about it then after a while it just becomes the norm and you wonder why it didnt happen sooner.