I can kinda see edge cases where 1-1 NAT makes sense, depending on the product, or are they asking for NAPT like most people think of NAT?

The latter, AFAIK. It has been some months since the product manager in question forwarded the question to us.

As for 1:1 NAT, we already support other solutions that have similar effects, such as scriptable proxying.

Nature will find a way :)

your client will probably have it's market eaten by someone who understand the tech. hopefully.

/me insert faster horse fallacy