Assuming you're talking about RFC 8981, then I don't think this actually helps as much as you would like, because typically you would have an assigned /64 and t

Assuming you're talking about RFC 8981, then I don't think this actually helps as much as you would like, because typically you would have an assigned /64 and then just randomize the low order bits, but the /64 would be static and usable as a tracking identifier, as noted in the Security Considerations. And if you're in an environment where you can have randomized prefixes, you can probably also have randomized v4 addresses.