As I said before, I've envisioned a pretty good map for one before—it essentially would consist of a Scourge- or Old God-heavy Naz'Anak-esque zone (especially now that we know how deep the Forge of Souls stretches), the outskirts of a sub-Ulduar complex that would be revealed to be Uldorus (possibly the same location as the former depending on the scale of it, since Naz'Anak looks exactly like what I'd expect the outskirts of the World-Soul containment facility to look like), a sprawling Nerubian city resembling what Azjol-Nerub should've been, a Drustvar-esque dark forest around the roots of Vordrassil where the Nightmare started and blends into reality (making the zone go increasingly corrupted and surreal as you got closer, looking more and more like the Nightmare in Legion), a massive Troll catacomb or city stretching beneath Zul'Drak (finally leading us to the end of the Snake tail and bringing back another cut element from WotLK, which was the Zul'Drak raid that was cut just like Naz'Anak was) and possibly a more pristine and colorful forest fed by currents seeping from Lake Winterspring and which pours water into the lower zones. One thing I always also pictured that would be interesting is that the zones are on different vertical levels, with a pristine forest zone at the top and Naz'Anak or Azjol-Nerub at the lowest altitude.
The Nerubians would be the primary colonies, but there could also be a Troll presence, a Nightmare presence, a Scourge presence, a Titan presence etc. and a variety of pretty and exotic-yet-grounded zones.