Bozja is a step in the right direction. A system they should splash all over the next expansion, in many of the open world zones. The core design of the critical missions should be a really fun and dynamic activity which should basically be a big chunk of the end game activity of the game.
Like I said, this could be where you have beast tribes summon their primals after you do like 100 fates. These primals drop rare mounts that already exist but with different colors or effects on them (like rain effect on a goobbue). You'd have to kill these critical event primals some 300 times to get the achievement that unlocks it. That would be great for end game in my opinion. But not just mounts, it could be other things like existing weapons with extra effects on them; just use existing whatever and they don't have to waste too much time creating new stuff.