Right. But isn't it so that each device gets its own IPv6 public address? So that PC1 and PC2 connected through the same modem are identifiable by different IPs, while you can still see that they're from the same modem/household? If that's the case, it can be a privacy concern.
Theoretically, even non-router devices could use more than one address, just to confuse what's listening on the other side.
In that scenario, DHCPv6 would be responsible for keeping the assigned subnet filled randomly, rather than being conservative and consistent with address assignments. I don't know if anyone is doing it now, but I don't think we should dismiss IPv6 for this reason.
