Yeah, that is indeed interesting!
Are we talking about “passkey attestation” here then? – Okay, those services that require only device-bound passkeys would be already “not many”, but “requiring attestation” would probably reduce the possible services that do that even more…
In the article you linked, there are requirements for “cross-device registration/authentication” mentioned… So, that would be QR code based then? (and maybe related feature request then: Support for passkey QR codes / CDA (Cross-Device Authentication)) PS: Just found that Note below there: “Users can’t use cross-device registration if you enable attestation.”… 
That was @rengle’s original request…
Hm, I think it’s not surprising that Microsoft does this… With their own services like Entra etc. they apply such strict passkey usage… they offer passkey “management” via their OS (Windows) and Windows Hello… 