after reading most of the posts here, I would add my opinion that "casual" content is anything that can be cleared with minimal learning and minimal attempts required to complete it. An example would be ANY dungeon because you can clear them on Day 1 with 1-2 wipes total and not be bothered with guides. Mechanics are typically very forgiving to mistakes.

I woudn't ever get rid of this in favor of harder content, though. This content needs to exist so players with limited time to play can still progress on something, even if its just collecting tomestones and never touching extremes/savage.

24-mans are kind of harder than dungeons, but for different reasons than how extreme/savage are harder than dungeons. But realistically, you can clear any 24-man with 2-3 wipes and not knowing anything at all.

(experiences will vary but that has been my case since 3.0)

So really, to address OP: adding difficulty will only add time required for most people, and I dont think that's where FFxiv wants to budge. I think they want dungeons to be 15-25 minutes regardless of skill and making them any more difficult will only add time spent by player learning how to navigate the challenges.

I think those of us that want more casually-hard content just have to settle with extremes/savage/whatever PotD2.0 is.