What I've failed to understand in this whole Google reCAPTCHA discussion so far: How is this is even going to prevent bot usage and increase security? What's going to stop a bot farm in SE Asia from running a fleet of Android devices?
Also consider this: While bot farms may be able to buy millions of Android devices, they will certainly attract a lot of scrutiny as they approach the billion mark. So bot farms will never own more Android devices than humans.
If you have the $$$, which the big guys certainly do, they'll just buy the bare attestation bits and figure out how to use them directly.