I am super happy to hear about a bit of challenge being added to open world content. The only real "open world" content that was suppose to be hard was hunting, odin and behemoth, but those are just huge zergfests. The challenge in hunting them is to be able to see them in the sea of people. Or not to crash the server.

Hopefully, along with hard mobs, they add more difficult open world bosses that have some sort of feature that doesn't allow zergfests. Maybe they can make it so that only the group who pulls it can kill it. After someone kills the boss they should get a 24 hour debuff that doesn't allow them to challenge the boss again. This will stop people from camping the bosses 24/7, keep the kill rare(something to strive for) and make sure it's not a zergfest.