Where sorcery is intuitive, wizardry is methodical and theurgy is assisted. This, unless I am very very mistaken, is widely accepted as D&D lore that transcends campaign settings. But once you introduce ki, psionics or incarnum, you have to go deeper into a theory of magic that may not be welcome everywhere.

Personally, I am okay with the 5e PHB's claim that all official settings have some version of the Weave, an ambient thingamagic that sorcerers, wizards and clerics are all reliant on, which may be tangled or torn in certain regions of the world. But I know that many people are not okay with that. Even among Forgotten Realms players, the idea that sorcerers do not have all the mojo within themselves, or that even divine agents would have trouble with a wild or dead magic zone, doesn't seem all that popular.

So if in your world, say, a sorcerer uses the power of their blood, a wizard uses the power of their mind, and a cleric uses the power of their soul (with divine guidance), then there is little room for monks, psions or incarnates. Well, monks still get to be martial artists, but ki is less special.

Quote Originally Posted by Duff View Post
You want to have stories of going to places so far from the normal that magic itself doesn't go there. But that's hard to balance* if you have some characters who've lost magic and some who are just fine
There is also the possibility of using areas where ambient magic works differently. Like a tower where highly-specialized arcane research was conducted, galvanizing a certain school of spells at the expense of the others. Or a planar manifest zone, where certain damage types become ineffective while others are maxed out. A psion would gain no bonus or malus from such an area.