What if the user only get one address, how to separate the two?
Seems like a need to share if a larger block (providor) is handing out based on blocks or single addresses…
Since /64 is smallest network in IPv6 and because of that most providers hand out /64 when you ask for IPv6 public address because A) Most Rate Limiting uses /64 and B) IPv6 has so many IPs, no one cares.
Vultr has at least one /32 I was able to find (2001:19F0::/32) which if you cut that into /64 comes out ~4.2 Billion different networks or same amount of IPv4 address that exist.
ARIN will hand anyone who asks a /48 IPv6 subnet which 65,536 unique networks and getting larger prefix is not hard.
A /64 is not the smallest network in IPv6. Nothing stops you having a /112 or a /126 or whatever you like.
It is the only network size on which SLAAC works however, so it's a good choice for lan sizes.
So from the point of abuse logic it's appropriate to treat the whole /64 as a single unit. (That was the starting point of the thread, even though I realize that due to thread drift that's probably not what your comment was about.)
This RFC has things that may not work properly not to use /64. https://datatracker.ietf.org/doc/html/rfc7421#section-4.2