[Sawrock]

I think, by default, all characters should have a chance to proc an evasion on an autohit (which the process of such will be called Reflex for further purposes in this post). If they do, it'd reduce the damage by Scaled CEL/2, as others have stated above. I agree that magic, by default, should not be affected by Reflex. I also believe the following should also happen:

Rogue's Evasion should be changed; it instead should be Main Class Only, and give +30% chance to the dodge proc for Reflex to happen against Physical Attacks only.
Void Assassin's Voidveil's effect should be changed to no longer be main class only.
Void Assassin should gain a new Main Class Only skill that I'll call Magical Reflex (1 rank). It should allow for magic to be affected by Reflex.
Mage should gain a new Main Class Only skill that I'll call Aimed Focus (1 rank). It would give magic (note, not magic damage skills, magic skills) +30% chance to the accuracy proc against Reflex to happen against Magical Attacks only, and reduce Reflex's damage reduction from magic by 10% (which would only work against Void Assassin's Magical Reflex, normally).
Archers should gain a new Main Class Only skill called Aimed Skill (1 rank). It would give non-magic skills +30% chance to the accuracy proc against Reflex to happen.