Interesting, when I looked at it a couple years ago I didn't see that. So it uses the PIV mode? And it can use asymmetric encryption as I see it?

This is definitely something I will look at. One problem is that I use Unix Pass ( https://www.passwordstore.org/ ), which uses GPG under the hood. Through that I use the yubikeys as the actual encryption source for each password, I have each password encrypted against multiple keys to safeguard against loss.

So what would be needed for me to completely move over to age, would be a version of 'pass' that supports age with yubikeys, and also a mobile app that can do this (right now I use PasswordStore on Android, which communicates with OpenKeyChain which is basically GPG for Android with a nice shell around it). So I use the Yubikey over NFC there (though USB is also possible if you really want), to access my passwords. It works pretty well after some initial hiccups.

Besides this I GPG for asymmetric-based file encryption of things like backups, for which age could already be an alternative indeed. And for SSH access, but I kinda had Fido2 pegged as a replacement for that as this is where they're seeming to be headed.

That's exactly the use case I set out to replace for myself. I'll put together a guide at some point. The part I don't use and so can't really own is the mobile app, I would love a community solution there.

I am also planning to integrate https://github.com/FiloSottile/yubikey-agent which makes the SSH authentication part very easy, so that you only type your PIN once and it stays cached.