If the FIDO alliance ever gets to the point where I can manage my passkeys on Open hardware, using Open Source software that I can edit in a way where I can manage everything that's happening, where I can recompile every part of the toolchain, and where that Open Source solution running on hardware that I control actually works with real websites and doesn't get denied by all of them over attestation concerns, then I'll pay attention. Until then, it's not really Open, not in practice, and it's not worth advocating for or using.
No, Yubikeys are not a solution to that problem. I can't flash a Yubikey with custom firmware and still generate the same attestation proof. I can't back up my keys off of a Yubikey or transfer them to a new key. It's just introducing another proprietary chunk into the mix. If I'm wrong about that and Yubikeys do support export and cloning, then great. But I'm pretty sure they don't.
As it stands, I'm not sure it's possible for any of my devices to use passkey login, and whenever I see people bring up this problem, they get told that the impossibility of general 3rd-party generic interoperability is on purpose, because it makes things more secure. Well great, but I'm not going to use it then. I can't use it.
Good hecking luck getting people to adopt that standard. More secure at the cost of "there is no way Open Source advocates are ever going to sign on to this" or encourage people to switch.
Maybe open clients will come out (although with hardware attestation, maybe nothing will work with them, maybe it'll be "Open" the same way that web DRM is "Open" because technically anybody could make a competitor to Widevine and try to lobby Netflix to support them if they hope and pray hard enough). In any case, until there's an actual solution (and not just a promise of a future solution) that works on a rooted, deGoogled Android phone without an additional hardware key, until there's a working solution that allows portability between ecosystems via user-controlled clients, it's not a standard that's worth paying attention to.
1Password is making a big deal over the fact that using them means this will work on multiple devices; they've been billing themselves as the solution to migration across ecosystems. I don't buy it. Is there any way to mass-export them out of 1Password? No? Then it's vendor lock-in for 1Password, you're just trading one ecosystem for another. There are no good solutions to this problem that have been proposed; simultaneously registering multiple proprietary devices in not a real solution.
It's not Open or portable. Not in practice, not in a way where actual users today can use it that way. If that problem gets solved, then I'll get excited about it. Otherwise, it doesn't matter how secure it is, it's still anti-user.