A certain nordic god recently bestowed upon me (or lent me) the gift of the Tales of Earthsea collection. It has my head spinning.
Personally, the Earthsea stories are my favorite fantasy collection. They really get inside my head.
Anyway, I was thinking that BW is close, but to do Earthsea true justice a few things would have to be changed.
First, the Will+Sorcery dialectic doesn't seem to accurately reflect the source material. Nor does Forte for Tax tests (I think).
So I think there should be a True Power or Craft attribute that represents the character's contact with the Old and True Powers. This attribute would then take the place of both Will and Forte in Sorcery.
Skills would be Hand, Summoner, Patterner, Windkey, Namer and Changer.
Herbal and Chanter are mundane skills--Herbalism and Ancient and Obscure histories.
Namer is a problematic skill, but there are some wizards in Mrs LeGuin's work who simply know the names of all those whom they see.
Spells of Curing and Healing (and a number of others) are not taught on Roke as they are left to the Witches. But they'd be available skill choices depending on lifepaths.
To work a spell, the Wizard combines his Power plus the applicable craft skill. To summon a magewind, I'd test my character's True Power plus his Windkey skill.
All spells are abstractions. Thor suggested this: Skills determine/act as impeti and elements. Origin, Duration, and Area of Effect are combined on the fly to create the obstacle.
I think Namer would have to be restricted to Single Target area of effect. Or something.
Tax is taken against True Power. As is sustaining. She often refers to her wizard characters as having been "broken" or "spent part of his strength for good" or not having "a shred of power left in me to follow him with." It seems like wizards spend their ability to call upon their power, more than they drain their vital energy.
However, I think that Forte dice should be able to be "spent" to buy off Tax. However, each die is recovered in 24 hours - Health (not 10 minus Health).
Playing in Earthsea would change around the traits for wizards and humans a bit. All characters would possess the Named trait. If the true name of a character is learned and spoken, the character must obey the command given. It acts like the Tasting the Lash trait. Or, if another effect is being called on, the Wizard who knows his target's True Name may add his Will exponent dice into his casting roll.
All characters who are Gifted possess a mild form of innate Sense. They can sense other wizards in their presence and sense spells being worked. All Gifted characters automatically start the game with Aura Reading opened at its root. It may be advanced normally if the skill appears in the character's lifepaths, or with General points if it does not.
The wizard's staff of Roke is a Sustainer and a Channeller. The Cloak is a Shunt (and warm to boot). All wizards who study on Roke begin the game with them if they desire. (I guess they'd have to cost rps.)