Nothing, RO e.g. has active and passive skills per Job that can be learned via quests.
However, I think it would be far better to create a whole new system (i.e. âMaster Circlesâ) where you build everything around it.
E.g. visiting a shunned researcher to learn about forbidden arts that were abolished when the treaty between goddesses and demons was written, or excavating ruins for clues on long forgotten techniques from the times before Zachariel?
There are countless methods where you could introduce new content (e.g. minigames like archaeological excavations where you can dig for clues on the past, historical research, interactions with the Class Masters to gain their favor and teach you more about the Class) that bring more lore, more fun and an actual reward for working on sth.
You need a whole system to continuously advance, otherwise you will just feel bored after finishing a single quest or leveling to new cap to buy another attribute.
Yes, it is much more work but currently the Classes are just dead, no more advancement quests, just a few attribute point quests that are pointless since you gain much more via events, and no real interaction with the lore except for a few individuals (e.g. the Chronomancer Master).
The whole problem comes down to the fact that IMC keeps adding new stuff to new content but neglects and forgets old ones (e.g. no special costume for the majority of Classes).
If Re:build doesnât address this issue and just keeps stockpiling, everything they worked so hard for in the past will be neglected and forgotten.