> Part of the motivation for this was to use (mostly) unique MAC addresses (48 bits) as your identifier and that fits in 64 bits. Of course this became a massive PII leak and a tracker's dream so it never happened but we're still stuck with /64 blocks that we absoultely do not need.

please read about rfc4941 privacy extensions & how prevalent their use is before continuing to regurgitate decade-old, outdated privacy alarmism about MaC aDdReSsEs.