As there is no longer an active community supporting CS-MAP, we're aiming in the future to look into the Esri reprojection library and PROJ. That being said, we will still continue to support CS-MAP as we know that a lot of FME users still depend on it. So we will work to make it easier and easier to use either PROJ or Esri (or CS-MAP) as the default projection engine in FME with time.

There's also a PROJReprojector currently under active development with a limited form of it available already in the FME 2020.0 betas. If any keeners out there are interested in trying it out, you can find it in our downloads/betas page.