shamelessly stealborrow some sections of it for my own homebrew?
I'm not entirely sold on the necessity of Temp-HP instead of DR, but you can probably just chalk that up to my lack of experience with high level campaigns.
I do have one or two little issues that are still niggling at me though. The first is linking the scaling of AC to BAB. The medium BAB classes (rogues, monk, TWF rangers) are in melee combat nearly as much Warriors and Paladins, and there is no guarantee the demon you're fighting won't turn around and try to gib them, or that the horde of orcs will all line up and politely wait for a shot at your party's meatshield.
What if we let AC scale just with ECL or HD, rather than BAB? Yes it means that wizards and sorcerers get a full Base Armor Class (BAC) but I can't think of a better way that won't penalize quite a few melee-based players.
The second thing is, since heavy armor is now definitely better than medium or light armor from a pure defensive point of view, can we either increase or remove the Max-Dex Bonus? At higher levels, it's restrictive enough that some Dexterity based builds forego armor entirely, and under your system that leaves them very (comparatively) squishy.
Or are you worried that higher Dex scores will combine with your improved AC to make some classes untouchable?