This isn't a build, just some idle thoughts I couldn't get out of my head at 4:00 am.
Elf Wizard 18/Rogue 2, dragontouched leather armor, Mithral large shield +5.
Pale Master.
Spell failure is negated due to racial enhancements.
The new shield mastery feat will provide a passive 15% reduction to incoming physical damage. On top of that, you have active blocking DR from the shield, and passive 10/adamantine from Stoneskin.
Evasion from Rogue, 25% incorporeal miss chance + 50% miss chance from Displacement.
With some effort, AC can reach a passable amount.
10 base.
7 Shield
8 Armor
7 Dex (16 base, +6 item, +2 tome = 24, which is max dex for dragontouched leather)
+1 dodge (Mabar cloak level 16)
+2 dodge (Bracers, either Chaosguard or the new ones in u9 that also have Toughness)
+3 dodge (Dragontouched sov rune)
+4 Insight (On greensteel main hand item)
+5 protection (Greensteel mineral goggles, I'm thinking? The redundant heavy fort + undead form helps against the newer enemies that have some fortification bypass.)
+5 natural armor on a pirate hat.
+5 from airship buffs
+5 from Combat Expertise (Off when casting, then toggle on when blocking)
That puts us at 62 already, then there's extra AC from active shield blocking. Not a ton of AC, but it's enough to put you in the ballpark for high level content.
That plus the fairly awesome straight up miss chance from wraith+displacement should reduce incoming hits to a trickle, while active blocking will handle the damage very well.
This character would toss an acid rain/firewall, keep death aura up, and sit and block in it.
I don't have much experience playing casters, but this sounds like it could be fun.
Thoughts?