If you need Onion Routing then you need Onion Routing. IPv6 Privacy Addressing gives you roughly the same properties you had with IPv4 NAT except now when you did want a stable address you've got one.

Multi address is much healthier in IPv6, so it's reasonable for your browser to even spin up an address associated with a Porn tab, and then destroy it again when you close that tab, while still using your other IPv6 address for a post you make meanwhile to Hacker News. It's also reasonable (while it was often likely to cause mysterious problems in IPv4) to give your local web server a long-lived IPv6 address while your web browser's address changes every hour.