Those kind of dungeons are very cool, but only make sense in a no-instanced game.

In theme parks like FF XIV dungeons are something to burn and finish fast, because... it's the most effective thing to do.


To make work those dungeons, people would need reasons to go and stay. Rare monster that drops interesting things, and so on.
In this game you can't make it, because no drop can be really that interesting, they always loose most of his value in a few months.