It means I can’t do a fully ipv6 backend, which is a bit irritating.
Why do you need ipv4 on your backend to reach ipv4 destinations?
NAT64 is NAT with all its associated annoyances and bugs, and proxies/caches are just annoying to maintain and a needless added point of failure for small installations.
If you have an bunch of servers using ipv6 to avoid NAT issues.