On the other, we don't want to create a situation where it's impossible to start a new passkey provider because you'll never get 1000s of websites to put you on their allowlist.
So far, we haven't done attestation for passkey providers at all. There is only the AAGUID, which is a spoofable identifer should any sites try to filter based on it. There are legitimate cases where sites are required to know more, but we're trying to find a path that doesn't lead to the problems that you worry about and, so far, are erring on the side of openness.