Would it be possible to put these things as server functions?
- Single quest completions, so people can't continually turn in a quest reward, maybe it's possible to have some better rewards that can only be obtained once
- Some kind of global quest variable - server wide events, some quests or events could possibly be completed only once. Like kill a dragon to trigger extra progression, only the first person can do it and it won't respawn. Some older games used this and it was pretty great for drama, cooperation, and stuff
- Quest cooldowns - to implement daily quests or otherwise
- Unique or unsharable rune combos in some way, maybe high level spells or "different" spells (self-teleportation to different towns? acquirable via having have had to visit that town normally in the first place) acquirable into your spellbook only via touching a book or reading a book in a quest, requires runes to cast, but can't be learnt via discovery, only by completion of something or touching an item