With IPv6 Privacy Addressing, the ongoing changing of IPv6 addresses (interface ID) maintains privacy by periodically shifting the Interface ID, so you already have privacy, without need to use NAT.
NPTv6 just changes the network prefix, keeping the interface ID intact on both sides. This is a low-resoruce, stateless form of NAT. Regardagless, that should not be needed here.
Before you look in to NAT66 for ":anonymity" and "privacy" you should unpack what the need behind the need is. What is the use case you are defending against? You may find that NAT does not provide the anonymity that you imagine it does.
NPTv6 is designed for VERY high volume traffic (service provider) so needs hardware support. NAT6 has no such restriction, but it is resource intensive.
What you are proposing is not the best practice for IPv6 networks.