Especially as if someone is able to capture ifconfig data, they can probably send a curl request to a malicious web server and expose the NAT IP as well.
Just because you can think of scenarios where the IPv4 setup doesn't make a different doesn't discount that there are scenarios where it does.
Someone being able to observer some state is a different model from someone being able to perform actions on the system and the former has many more realistic scenarios in addition to the ones of the latter.
