Good idea, BUT: my last info is, that the FIDO2 credential Bitwarden uses for it’s 2FA, is a ‘non-discoverable credential’ and therefore not a passkey, altough Bitwarden (falsely) labels it (still) “passkey”.
A passkey is a ‘discoverable credential’ - and don’t confuse it with “login with passkey” from Bitwarden… the latter credential is a passkey = discoverable credential, that get’s created.
(BTW we had that discussion a few weeks/months ago on Reddit with Mika and Ryan from Bitwarden, why Bitwarden “falsely” labeled it that and I critized it, because it leads to confusions like this one. No offence. 
My last info here is “the team discusses it”…)
PS: And I guess I wanted to say by that: the FIDO2-Bitwarden-2FA can’t be “syncable”, as it is a non-discoverable credential - and not a (potentially syncable) passkey.