I can imagine a weird contraption of a custom DNS server that tracks client requests, returns unique private IPv4 addresses and simultaneously tells to some NAT

I can imagine a weird contraption of a custom DNS server that tracks client requests, returns unique private IPv4 addresses and simultaneously tells to some NAT-PT engine that this source IPv4 address talking to that destination IPv4 address needs to be translated to that IPv6 address. I can imagine this to be extremely fragile and break whenever an IP address is looked up using any different manner than plain DNS (e.g. by having IP in API responses, or just using DoH). Yet, I can imagine someone's probably already working on this abomination.