Quite a few German freight wagons (including, but not limited to, the Tharandter Rampe Roos-t, the Linke Rheinstrecke Shimmns-u, both the LFR and BRO Tadgs) aren't available in loaded versions for use in Formation Designer. It would be quite nice to be able to make loaded freight trains too...
That's interesting and sounds very similar to my beef with Livery Editor whereby my TEA tanker liveries (NTP) only get applied to empty versions of the wagons too. (I'm guessing that the game sees empty and full wagons as two different things?).
I watched Matt's video on Formation Designer late last night and he did mention the subject of loads. He said that there would be a toggle switch (presumably Empty / Loaded) against all appropriate wagons to select which version you want. So that is good news