It doesn't seem to be fundamentally different than reCAPTCHA. They will probably replace the click-this-checkbox box with a set of elements already on the hosted page. Only indexing a page's HTML isn't good enough -- it's better to also know how people interact with the HTML. Unfortunately, as soon as they click a link on Google, Google is no longer invited to the party, and is blind to how the user interacts with the page.

The next best thing a search company can do is have every website willingly track their users' mouse and key movements, and then willingly send all of that data to the company's inbox. In return, Google provides them with a binary classifier trained on all of the user click-stream/click-move data which determines whether or not the user is a bot!

It's an OK deal for the website owner; it's a great deal for Google. Not to mention, the user is now sending anonymous data to Google, at the expense of the website's Privacy Policy.

Google gets website owners to willingly install live-cameras on every corner of their website, and then willingly send over all of the footage, in exchange for "protection" from bots. Cough The Government gets citizens to willingly fill out lengthy tax forms, and then willingly send over a bunch of money, in exchange for "protection" from criminals. Cough