Probably the most involved part of this conversion is done: Arcane Magic
What I was going for here was to emulate the general Defiling/Preserving dichotomy from the original game, while actually having rules support for the idea from the game fiction (and the recent 4th Edition D&D) that Preservers have the ability (and the temptation) to defile for quick and dirty magic. Defiling is presented as the “natural state” of arcane magic while Preservers actually need to take extra steps to do things the right way.
The fact that Defilers don’t have any Difficulty associated with their spells is a major boon to them, and one that gets higher as their magic gets more powerful. I basically threw game balance out the window with this, which I’m OK with, because high-level Defilers are better intended as major antagonists and not player characters. If you’re thinking about having PC Defilers, you might want to dial that back to “spells have half Difficulty” in order to stop it from being a no-brainer choice.
Levels? Spell Slots?
Removing character levels from the game is one of the main design goals I have here, though magic itself has an intrinsic level system, using the spell’s Intensity. The compromise of magicians having to buy their way up Intensities and expanding their daily spell slots with the Spells advantage actually makes things less class-ish in my mind, since a character might take the bare minimum of casting ability in order to dabble in magic, while the alternative would be something like a 5-point “Arcane Magician” advantage that would be a high bar that characters would only both taking if they were going to be dedicated magicians.
Other Supernatural Stuff
Elements of this system are going to find their way into Psionics and other magic-like powers. Just about everyone is going to have powers with Difficulty equal to their Intensity, though the spellbook flexibility of arcane casters here is going to be their “thing.”