Be that as it may, they can still roll out the passkey attestation requirement gradually, -- "flip the switch" just a few thousand users at a time -- so that at no one point in time is there a large blip in users. Truth be told, tech platforms don't even really need to measure what portion of users' devices support remote attestation, since the overwhelming majority of devices will support it. They just need to know that users are passkey-capable in the first place; once enough users have passkeys in any form, they can start requiring remote attestation.

As for the browser permission prompt: Firefox simply warns you that the site is "requesting extended information about your security key [sic] which may affect your privacy." [1] It does not make it at all clear to the user that what's really happening is that the website is gating acces behind a specific approved software stack. If I use a non-widely-used OS or device, what website is going to approve its attestation credentials?

[1] https://github.com/mozilla-firefox/firefox/blob/8e9ac3e12bba...