You need NAT whenever you can't change your peers' routing table, for whatever reason.

It's used extensively in IPv4 world for LAN=>WAN connectivity because your only peer (your ISP) won't agree to send all traffic for 192.168.0.0/24 to your home.

Its most popular use case disappearing doesn't make it any less useful for the narrow set of circumstances when it's basically your only option.

NAT64 is NAT in reverse, essentially. Your internal, IPv6 network can use it to contact an IPv4 host by embedding the target address. This is arguably better than current NAT44. The NAT64 only needs to track which ports and IPs are used on the IPv4 side which should become easier as more hosts don't require an IPv4 anymore.

It's a last-stage transitional method IMO, when most but not all of the internet is IPv6.