I admit it, I only want this (or something that lets you stay centered in armor & shield from vanguard/defender trees) so I can armor up a monk, and yes, I know everyone thinks monks are overpowered as it is, but I'm not sure how big of a deal this would be:
-It would, obviously, require 8 levels of fighter (or paladin if you allowed it from vanguard/defender?), eating into monk levels
-It would be effectively limited to light armor and shields, or do without evasion, which seems like a balanced trade-off
-It would limit the usefulness of Wisdom, since you can't add it to AC, further reducing the effectiveness of monk abilities
-It would exclude using kensei to remain centered with non-monk weapons, so unarmed, kama, staff or shortsword
Mostly, I'm still looking for a good excuse to make a finesse monk.