It’s building on Scenario Mode from ye olde Trust system.
Some duties let you pick your party, though Realm Reborn duties have fixed parties according to your role.
Future updates will expand Duty Support to include duties “for 2.x to Heavensward and beyond”.

See theFF14 patch 1.6 notesfor more on everything.
We’ll tell you FF14 is not only one of thebest MMOs, it’s the best.
