Quite a bit of that already exists, actaully.
The characters do loose health from bleeding. OG has two 'health bars'. Temporary damage is caused by blunt impacts while permanent damage is caused by sharps and heavy blunt trauma. Temporary health regenerates, but can never regenerate higher than your permanent health. It doesn't cover bones breaking or actual blood volumes, but it does a good job estimating the effects of impacts. No bandages as of yet though. I doubt we'll see them, since OG is primarily going to be level based. I imagine Turner's state will be reset after most levels are completed.
You can simulate battlefields yourself, with the level editor. The engine does just fine, the limiting factor is your PC's power. You can spawn whatever actors you want, assign teams and let events unfold.
Air attack and arena: show
Extra combat techniques are simply compilations of attack animations. There are already a few mods that include new attacks. The Tengu is the first to come to mind.
I believe David has partner AI in the plans somewhere, but I could be wrong. There is a mod someone was working on for it though.
The only one that isn't really there is the trading thing. Because OG is level based, there is no market anywhere and the ability to purchase really good weapons before a certain level could break the David and Aubrey's ability to construct well-balanced levels.