One of my all-time favorite pieces of third-party content is Spheres of Power from Pathfinder 1e: in short, it bundles magic and might into a number of discrete domains called spheres, each based around a specific theme. This then lets players build characters around a specific theme or subset of themes, rather than large spell lists or the like. In a recent thread, I and a few others talked about how a categorization system of this kind could have helped make feats more forwards-compatible, as classes could easily have been assigned broad feat domains that would then have class-agnostic feats assigned to them later on alongside their own unique, class-exclusive feats.
One of the prevalent opinions in that thread was that shifting 2e to a spheres-like system for feats would be too massive an undertaking to do successfully. I personally agree with this, but nonetheless feel there's still room to at least engage in a fun thought exercise: suppose we were to take the spells and feats in 2e and categorize them into domains, smaller than a tradition spell list or a class feat list but large enough to cover a broad theme. What would it look like? Specifically:
These are questions I've been playing with in my head for some time, and I'll be keen to hear from others as well. Part of me very much wants to key spell domains to divine domains as seen on the Champion or Cleric, especially because it would make it easier to completely reorient the Cleric's spells around their divine domains instead of just giving them three extra spells they can prepare, but I also feel some of those domains don't map as well onto spells as others, like cities or confidence. How would you go about doing this?