With hardware tokens, yes, I use that. I was thinking that building it on a web server would be really handy with an integrated client you could use with iCloud, Windows Hello, etc.
With /passkeys/, actually! It's more generic than just hardware keys. I don't know of any good implementation yet, but there were a few projects on github mentioned in some passkey-related discussions here.
I do not use anything like iCloud or Windows Hello and I don't know what these services actually use, but if they implement these open standards, it's only a matter of adding some glue code. I'd say it's likely that Putty will implement this over on Windows eventually. That is my speculation, as I said, I don't actually use any of this.
I mentioned those because key management is the hard part and most people are going to be using platform authenticators for that reason. In some cases there are APIs (this was one of the features in the last macOS / iOS release) but I was also thinking that moving it closer to a browser is interesting because between platform passkeys and SSO, there are a lot of people who have all of their credentials & MFA ready in a browser and would like to reuse that.
Some searching suggests there’s at least one implementation of the SSH agent protocol using Windows Hello, which is great.
