first step towards providing visual anonymity for video on YouTube
Slap a big disclaimer on that!
It's visual anonymity from everyone except Google, they still get the before and after footage and they know how valuable ALL information is. Anyone with legal interest or a want for metrics data knows their number already.
Actually by using the blurring tool you're attracting attention to the video and making it easier to vet the videos for possible faces of interest. Google will surely get a lot of requests for the unblurred versions by various agencies. Still, it's a step.