1. The old sewers in Regalia are still open and incomplete. Perhaps they can be reworked and the look updated?
2. There's also that big flat field by the canal and Dr.Fong's tower.
3. If anything else needs to be added, perhaps a hidden pirate cove with an island and ships out in one of the corners of the map.
4. An underwater kingdom for Maiar when the new Aquatic Update comes out (the conduit can be used to breathe underwater) would be nice, especially with the new plant life and coral reef!
5. A Starris meteor, with its own unique dungeon or just really cool, mystical environment.
6. A bit more terraforming detailing for the outer Regalian structures in the wildness.
7. A spooky Dracula-like castle on a hilltop out amongst some dark woods in one of Regalia's corner.
8. A GIANT map-wide sewer system with secret caves, sunken catacombs and hidden elven dungeons spanning the whole underground map.
9. Add an underworld under the map, with maybe nether ruins and such to inspire role players to dwell into void lore.
10. A dragon graveyard.
11. Airship landing pad and maintenance shop
12. A wildlife nature preserve.
13. An intact/ruined ancient elven city
14. A fragment or museum displaying the older, deleted worlds and what their biomes originally looked like.