FATE chains.
FATEs that have an effect on the world around them.
FATEs that unlock S rank hunts.
Shared currencies for FATEs.
These things all exist already.

When ShB released, everyone was doing these FATEs. Beating Archeotania was a pretty big deal. Everyone wanted the frog suit and the robofrog mount.
The issue isn't that the content isn't implemented in the game, it's that people just don't do it any more, and you can't do it on your own.