I don't see any requirement to support hardware attestation in the recaptcha documentation, the Play Services seem to be "enough".

I think it's most likely to be attested by Google remotely; they might be using an app (with enormous access to the phone as the Play Services have) to be able to link a ton of data together, possibly including the local activity on the phone, officially to make better humanity assessments based on it all.

For people using a Google account it probably won't make a huge difference, in terms of data collected.

If that's how it would work, spoofing would probably be theoretically possible, but it would be easy for Google to detect attestations used by multiple people.

Let's not forget that this is an update to a very approximate system, absolute security is not (yet) required.

But there's a good chance that it will be extremely hard to sidestep, despite that.