I can't say I see the appeal of a dangerous open world.
For me open world content is stuff to do solo while I'm waiting in DF (like daily hunts and beast tribe quests) and I don't particularly want those to take longer or be harder.

I don't think casual and hardcore necessarily has anything to do with difficulty.
To me casual means that you probably don't play every day or you only participate in a few specific activities while hardcore means that you invest a lot of time and effort into the game.

For myself, I play a few hours everyday. I spend most of my time on easy content such as leveling alternate classes and running dungeons with my FC.
I generally only try the more difficult content once it's on DF. I will likely never try Alex Savage since I already got the story from normal and am not really interested in challenge.

I wouldn't find a more difficult over world more rewarding. I would find it an irritant just slowing down my activities.