Great idea to use it for magic! One of the mechanical challenges to making any magic system is making it actually feel "magical," i.e. different from whatever effects naturally-occurring skills and equipment can have. If having a sweet magical sword gives me +2 to attack, but flanking my target also gives me +2 to attack -- well, what's the magic, exactly?
But if you have a radically different mechanic that *only* happens when there's magic -- that's a special feeling.
I'm thinking this would work well in the gritty swords & sorcery setting I've been contemplating, where D&D-style adventurers have already reached such crazily high levels that they basically have amassed all the worthwhile wealth in the world, and are now stomping down the populace to make sure nobody can ever threaten their preeminence. The PCs would be hard-hustling street rogues, scruffy two-bit hedge wizards, or laid-off ex-guards, trying to keep food on the table without attracting the notice of any 20th level Epic Murder Hobos.
