My suggestion would be to focus more on just boss FATEs and have them spawn with a greater regularity, and I am not talking about the normal boss FATEs, but the elite ones, e.g., Chi.

I do like the idea of an open world that borrows from Eureka though. Regularly spawning, and the thing that most people are missing out with on Eureka, is that even if it isn't exactly innovative, it gave people a regular excuse to actually go out into the instance and farm monsters to spawn FATEs, and the way this would function is that it would funnel people more actively into the open world.

Hunts do this to an extent but not even to the fraction of what a Eureka system could achieve, IMO.

Doesn't need to be innovative, but needs to give general people a reason to actually go out into the world, that isn't just... Gathering or daily tribe quests.