This is something I miss from XI, how you could go into and explore dungeons when not doing a quest or anything and you could pass by other players when just killing random monsters.
With open dungeons it could add a couple more things to what we have already.
Such as: Normal level mobs to just kill. Depending on the area the dungeon is in different Disciple of the Lands could come in to get materials. Random Fates in different parts of the dungeon. And of course Notorious Monsters.
Not only that, but don't all dungeons have someone standing outside them? Maybe have them be able to give levequests for that dungeon to do as well?