Hmm, I hadn't considered the avoidance of ASF. The void disciple isn't proficient with armor, and loses the benefit of mage armor and Wis to AC if he wears armor, but a gish character would be rocking it in mountain plate by level 5 if he really wanted to...that's not what I intended. How signficant do you think it is? A fighter 1/void disciple 5 is ready for most gish classes, and could wear plate mail and a heavy shield, gaining +11 AC w/12 Dex. Alternately, a fighter 1/void disciple 5 with mage armor and shield, and a 12 Dex and 12 Wis, would have +10 AC...although only +6 if he has no time to get his shield up.
It's good defense...so is that a strength that makes the void disciple more versatile, or an imbalance that makes it overpowered?