A lot of US based customers rely on NAT-PMP. Although personally I would much prefer uPnP, Apple devices do not support uPnP and hence a large part of the American market does need NAT-PMP.
I'm an Apple application developer (based in AU) and I use uPnP but my apps also need to support NAT-PMP to work in the US.
Whilst we refer to NAT-PMP, it has actually been replaced by the more modern Port Control Protocol (PCP) which is backwards compatible to NAT-PMP.
It would be a great to have PCP included in routerOS.
https://tools.ietf.org/html/rfc6887