Hi there,
So … Great news the first moves for FMD for the nRF52840 is now added to the newest SDK 2.7.1
the basics are , there is testing keys available, You only need to register your device if you plan on making a finished product. it is similar to signing up to Google MAPS API.
When I have more on the Coded PHY and the other supported features of FMD and as it comes out, STay tuned.
GL 
PJ 