I understand your position better, indeed. Thanks for taking the time to explain! You’ll be happy to learn that what you describe, EUI-64, is not the only way to generate an IPv6 address. The router will give you the prefix in any case, but there is the Stable Privacy Addresses scheme if you want the link-local part generated automatically, and you can set up a static IPv6 address (or several) on your machine, and the router will just have to shut up and deal it to you (for the local part, the prefix is still coming from the ISP)

Why not on IPv6? If you received a /64 from your ISP and pick only one IPv6 for Tor, I don’t see what the issue would be…