Spellpower plate is the only real sticky spot left, in my opinion.
[Divine Armor] rank 9,001: Increases armor granted by all gear pieces by (insert mathematically derived appropriate number here)
^ add a lower tier holy pally talent along these lines that would bring mail spellpower armor values to as if you were wearing plate and itemize mail such that its attractive to pallys.
there are kinks. Tier loot.... you would have some very confused tier vendors..
potential exploits in pvp, wearing tanker plate pieces might make you a god among rogues and other mele classes...
/shrug just a thought.