I don't think the main challenge is building this system, the main challenge is getting enough people using it to make it worthwhile.
Personally I think it should be a government provided service, not something with a sign up fee. There's actually no point at all in building this if people have to pay to use it, because they won't
> Will they interoperate with foreign governments?
Ideally, yes
But you're right, this isn't likely to happen in real life and I'm just being wishful. Instead we're going to get the much shittier capitalist version of this where every company and government spies on us and we have no expectation of privacy online at all
My fear is something like this WILL happen in some places and complicate the world as a result, or at worst isolate access to specific countries with similar laws on identification.
Personally I think it should be a government provided service, not something with a sign up fee. There's actually no point at all in building this if people have to pay to use it, because they won't