Culturally impossible as well, in the sense thar x.500 expected that every country's national telecom operator would take on the task of handling identity and certs for the population of that country.
That said, the US DoD had a pretty good stab at it, and even today in corners of the defense industrial base you can find companies like Isode that still service that niche. To be fair, x.400 messaging and x.500 directory looked pretty smart back in the day when smtp and passwd were the alternatives. It's just that smtp grew up incredibly fast and quickly outstripped the alternative.
I got my start in that era and they only looked smart if you didn't look deeply. Too many options, too many areas where they created a problem and then passed it off to someone else to fix.
