Divination is probably the hardest school to write, develop, and use.
It’s your “spot the plot” magic tradition. Players will inevitably (see what I did there?) ask questions about future events that you can’t possibly know or predict. And so it must be in most games that divinations are neutered, often worse than useless. Prophesies are vague or pointless instead of mysterious or baleful.
If the GM is trying to run a mystery plot, a divination spell might ruin everything by telling the PCs exactly where Jack the Ripper is, or the identity of the killer.
Honestly some of the problem just comes about in trying to reconcile a two-axis alignment system with the ability to see the future. If Good characters can know the consequences of their actions, how do they ever “fall?”
For this reason, it’s important to understand the difference between “choice” and “consequence,” and further creates a need for an “uncertainty principle.”
A character may learn the choices they will face or the consequences of their actions — but never both at the same time.
I’m thinking seriously about how I might use the violation of this principle as the basis for plot generation, a la Dogs in the Vineyard. A ritual caster learns the results of a choice they will face, which creates ripples of consequence.
Not sure yet, but I might seek this for all seven schools of magic.
Anyway, back on topic…
I’ve researched the subject pretty thoroughly over the last exty years, and I’ve devised a number of rules and tools for developing the schools of magic. At this stage, it’s honestly more of a victory dance than a genuine project.
There’s a lot of writing involved, so it’s still a project.