My ideal magic system would tie into my ideal game world of hyper advance AI controlled world. Players would be able to create their own magic and with right techniques, it can become very powerful. Singular events can also happen and players may inherit extremely powerful magic from worldly beings that no other players or very few lucky enough can get. (Think of the Dragon Slayers inheriting Dragon Slayer Magic from their dragon parents in Fairytail as an example) These players may teach other players their powerful magic or keep it for themselves to reign supreme. Or they can teach their guild certain magics that is unique to that guild. Those guildmates may betray and decide to teach outsiders those magic so players have to be cautious who they teach magic to.
In Wuxia world, each sect have their own special combat styles. Sect leaders and top martial artists create their own special skills and share it with nobody except maybe their decedents or leave it written in a book for someone fortunate enough to find it. Books containing those powerful moves would cause chaos because everyone is killing each other over the book.
I believe this kind of magic system is very hard to regulate with human overseeing the world because it requires a true living world of unpredictability and constant changes. (Not some fake living world GW2 claims to be) Only a hyper advance AI that can constantly regulate a world like this can make this possible. Considering technological advances growth is exponential, this kind of AI may be possible in at minimum 60 years from now which is when I might see this.






