Really like your engine! Don't get me wrong, I'm not trying to copy your game, but this "behaviour" would be something other C2 game designers might be interested in. Maybe you could make a plugin out of it, if you have the time? I'd enjoy it!
Just a little critique on the sketch of your archer: He seems to be right-handed, so his quiver should be worn over his right shoulder, too
Otherwise he wouldn't be able to pull his arrows out of it. These are little things one has to think about.