At the moment FM can access entity & block NBT to use in the NBT placeholder. It can't access server NBT storage, because that isn't exposed to clients by default.

If FM is installed on the server, it should be able to provide server NBT storage data to the client mod when requested, allowing the NBT placeholder to access it (which would be great, as that's a lot simpler than the current workaround of storing the required data on signs and accessing it that way).