UPDATE:
I am pleased to report success with our session yesterday. It was only our 3rd session with this new campaign, and the PCs had 3 battles (8 kobolds, 3 kobolds, and 4 kobold guards + chief + 3 consorts).
In the first fight, after only 2 kobolds were actually "killed", the rest defeated and surrendered. In the second fight, just 1 kobold was killed (by a critical hit), and only 1 was killed in the last battle...the rest either knocked unconscious or surrendered, etc.
So, only 4 out of 19 foes were actually killed. Now, a lot of this is narrative just by making going to 0 hp "defeat" (surrender, flee, etc.) or unconscious. Only those who went to 0 on critical hits actually died in the combat. It just seemed more "real" and less generic than "dead, dead, dead, etc."
The best was when 17 kobolds were rushing the party after they defeated the chieftain, the half-orc fighter held the body aloft while the gnome cleric spoke in Draconic for them to surrender/flee. They failed morale and ran.
After further discussion, our house-rules will be revised a bit more, but so far I really like the narrative difference, and the difference it makes to the story when the party returned with over a dozen prisoners instead of a dozen corpses.