[uberdru]

I'd put it slightly differently. The infrastructure went part of the way. It needed several more iterations. The UX, as you point out, never went anywhere. At least now people are getting comfortable with the idea of using a private key, even if no one has yet cracked the problem of crypto UX.

[dboreham]

When I say it was implemented, I mean at Netscape around 1999 we had projects with banks where they issued smart cards, used with USB readers, that facilitated SSL client cert auth. Similar to today's FIDO2/U2F. I don't know why these schemes were never widely adopted but it wasn't because the implementation was lacking.

[tatersolid]

I used these all these systems, and even helped run a smart card conference back then.

The implementations were very lacking. As unusable as PGP for normal people. The banking industry took a hard pass on the whole thing for good reason.