It rotates about once a day in most operating systems. Called ipv6 privacy extensions. This is of course defeatable, but it provides a nice black hole for a device. It moves on and you can't connect to it anymore.
On a protocol level, there is nothing in ipv6 preventing you from doing NAT. There are only less implementations of that, but it doesn't need buy-in from your ISP, as long as you control the router (and if not, you put a second router behind the first one which has your actual network).
I work for a large online service. We barely need your IP to track you. There are _so_ many other variables sites can use to track you. Even when you switch networks completely.
It's not a privacy nightmare. You could just run a proxy on your gateway and your connections would legitimately end up coming from it, but it wouldn't actually do much for your privacy.
Rotating the IP to get similar privacy to what NAT/PAT gave you is annoying I know with v6 we need to use DNS but I hate to say it. I miss Nat I hope the just give us nat66.
You are mixing up IPv6 prefix rotation and IPv6 privacy extensions, and you don't seem to take into account that IPv4 from most ISPs is much worse (typically, you get an IPv4 address from your ISP via DHCP and keep it nearly forever, nothing to defeat).
