I don't see why XI's HNM system is what people think of when they think of open-world content? That was one fairly specific thing.

That aside, rather than claiming why not change it to be something like:

-World boss spawns, weather changes or notifications made in cities etc.
-People start fighting boss, as more come boss gets stronger, gains new abilities and generally becomes more powerful.
-Boss is defeated! Everyone who participates for a certain time etc gains experience/company points/currency that can be spent on new items. Similarly to Odin coming out soon, the more bosses consecutively beaten would result in even more challenging encounters and more points rewarded.

Obviously being judged on participation is something that can be abused a bit, but it's definitely workable. Especially if you have to stay in range and the boss uses a lot of area/ground attacks that you need to keep dodging etc.

RMT could get involved if they wanted, but it'd be pretty useless considering you'd be trading currency for character-bound items.