Also the US reserves the right to demand ID if you're within 100 miles of a border - which is effectively 2/3 of the population. And detain you until your status can be "verified", however long that could take.

That should only be for non-citizens, but I have no idea how you could prove that without documentation in the first place.

So for the vast majority of Americans, you probably have to be carrying ID at all times anyway, else you risk someone deciding you "might" not actually be a citizen.

If this same rule was enacted in the UK, there would be no place on the British Isles that would be excluded, as nowhere is more than 100 miles from the coast.

In France you have to carry a state issued ID regardless of your location within the country. Driving license might be asked to be provided if there is an assumption you have one. A lasting legacy of the 40s.

In practice the pseudo-crime of being "suspicious looking" also requires ID. Good luck if you want to argue your constitutional rights. Immigration status is topical for the current era. Something as benign as walking up the street to pickup takeout could involve identifying yourself to the police and waiting for them to clear you for warrants.