Hi,
Read fvwm3 milestones on GitHub. Main new improvement is full and dynamic RandR and multiscreen support, and major configuration paths of “global” and “per-monitor” view of desks and pages.
You can freely clone fvwm3, build, install and then participate in testing. With or without NsCDE. If you want to try NsCDE with fvwm3, I suggest you first try it with fvwm 2.6.9 to become familiar with how it functions and so, and then you can edit /opt/NsCDE/bin/nscde to change FVWM_BIN to point to fvwm3 and login to that. Then, you can test adding monitors, changing new DesktopConfiguration between global and per-monitor, test FvwmPager etc.
See issues tab on github of fvwm3, so you can see on what bugs there is currently some work done.
Here is the official call for testing from developer: