Right now, many games end with heroic quests for the last hidden villager of your opponent.
I would like to see a technology similar to Spies in AoE II and AoE III, and Omniscience in Age of Mythology.
After researching Spies, the Line of Sight of your enemy is shared with you. This way, you can easily finish off the last few units without having to scout the entire map. If it’s the same as in AoE II, it would be 200 gold per enemy villager, with a minimum of 200 gold and a maximum of 30,000 gold.
Adding this technology to the Government Center would make the most sense. Devs would have to disable it for some of the campaign scenarios of course, especially those where you start in Iron Age.