Because they pinky promise? It'll be required to produce one like producing a driving license is required, but you don't need to have it with you. It'll be required because pubs/bars etc will require it. It'll not be required like giving a traffic stop breath sample is not required or like giving up your password is not required.

Imagine it was called IrishID or similar, help you to have empathy for how half of NI residents might feel about Brit-anything?

I guess it depends on its design (does it set up the dystopian infrastructure or not) and then more so on the legislation around it. It's already not uncommon to need your passport for work, making it a law to produce for any work would be the actual thing that changes this.

I get your point about IrishID, but be realistic, none of this is surprising considering the current state of things. I could make some controversial statements in this regard but I'll avoid the flames (I sympathise with you before you place me in the wrong box).

Huh? Everyone carries their phone everywhere and an ID card on an app is carried everywhere. When you stay at a hotel you might have to produce it, go to a doctors appointment,... and so on

Huh? In countries like Italy it's actually mandatory to have a form of identification on you when in public, this isn't the case.

The "brit_card" is on your phone and you will carry it everywhere. It is also a walking surveillance beacon and hacking target.

You could but you dont necessarily have to, no different to your passport or drivers license. The technical implementation remains to be seen. It may even be more secure than some forms id, such as those with NFC/RFID built in.