Can s/e actually make a "dungeon"?

[Eisenhower]

If Square were to make a dungeon like this, there would have to be a few rules [...]

Pretty much this. A segmented dungeon that holds rewards separated from the mainstream tomes and gear would be the most viable solution in my opinion. Like the title from BCoB Brutal. If you place cosmetics or housing items in there, you can be damn sure people will end up farming it anyway. Finding a good incentive that doesn't fall into farming will be difficult.

Right now, the "dungeons" we face are more akin a gauntlet of monsters with a chest at the end. Halatali HM was an interesting twist when it comes to the nature of the enemies we fight, but that's about it. To have a challenge-dungeon akin to Qarn, but with a sprawling, maybe even procedural map would be very fun. Having traps or environments that require you to have a certain class or take another path would be cool as well. Like a pit that a dragoon can jump over and then lower a bridge for the group or a set of locks that requires a Fire spell to open.

I think those that find this kind of content enthralling also prefer content that has a certain amount of replayability and novelty with each new run.