"IPv6 has had privacy built in for years now, on every OS available. Your inbound address will remain static and possible MAC address derived, but unless you're hosting anything on it (or disabled your firewall) your network traffic will be perfectly private."

I've tested with IPv6 on and off on several machines over the course of months. Google's search results become wild and unpredictable on the same machines soon after switching to IPv4.

My theory is that they rely on that IPv6 address to know exactly who they are providing results to and thus selling to.

If that theory didn't hold water, there would be exactly zero difference in search results after switching to all IPv4.