Treasure Hunt is the best place to start to expand with open world content, particularly pop-able NMs. We already have the base system down. Everytime you trigger a map, your entire party is locked in an open-world duty status (kind of like doing a leve) so no one can interfere. Great. Now let's see how I think SE can expand on this.

1) Have gatherer able to gather small pieces of a large rare map.
2) People can gather or buy these pieces (in 10s, 20s, 30s+) and combine them to get a rare map (think BCNM/KSNM in FFXI).
3) The map should encourage players to explore in various landmarks around Eorzea.
4) The rare maps should be challenging enough that would require 8 man to be on their toes for at least 7~10 minutes.
5) Drops crafting mats, housing items, gils, gears, mounts, minions, all you name it.
6) The reward, of course, will be proportionate so that the 8 man party that spent their time and resources isn't losing out against the gatherers who just sell their map pieces.

Now one of the community rep had already mentioned that treasure map system will be expanded in the future so hopefully things will be interesting enough that it isn't just a boring zerg grind like the current maps.