Interesting. Or they're doing both, actually. Have the landscape prepared so it's polished enough when new regions become accessible and you can take an early look at Sauthfarthing landscape. AND start preparations for the Southfarthing anyway, since maybe that's where we go next which would be very likely if we assume that we're actually getting Frodo's journey back home as the continuation of the Epic (only we take the detour through this new landscape rather than continue to Eregion). I can actually see this work very well story-wise. Gandalf, Aragorn, Frodo and company hit the road through Dunland but it makes Aragorn wonder what the heck is out there, on the "Royal Road" and shares his reasons why he wouldn't risk taking that road, not yet, until we scout it for him so he has an idea how to handle that place, now that he is king. Since all of the half orcs are purring from there... it would be an actual backstory/setup for the Scouring and setting a stage for the final Saruman's character arc. Maybe. Since the Royal Road is seemingly such a huge piece of content, I wouldn't leap into conclusions that it's just "random" simply because they want to fill-in-the-gaps. That, and a potential tale of the Forging and Eregion.