First suggestion in a while. I haven't seen any like it while using the forum search, but I apologize if it has already been suggested.
The core idea is to add hidden sites where a battle has occured in the past. Something like "You have stumbled upon [an ancient/a somewhat old/a recent] battleground", in the fashion we have for lairs now.
The older the batle, the harder to find it. It would also track ambushes, first the ones involving the player but also the other ones once bandits can attack caravans on their own.
The goal would be, for example, to find your old dead aventurer, take his sword and loot, or retrieve any possible survivor from his party.
It would also be useful for quests such as "my son went to fight for [adventurer], but it has been 3 weeks since he was last seen. Can you find him and tell me of his fate ?", or more important ones like "this caravan was carrying an important dwarven steel battle axe, but never made its way to its destination. Could you find it ?"
As an addition, I suggest loot stay the HELL attached to the corpse that used to wear them (because I find it a huge mood killer and really not handy), and that when, as an adventurer, you leave an ocurring battle (either fleeing or dying), the appropriate number of rounds is automatically simulated the moment you come back, depending on how long it's been since you left. Currently, you can flee, heal your broken arm, and come back 2 weeks later only to find the battle still raging on.