The Tech Tree mod uses Wesnoth's progression system to establish a simple tech tree, which is compatible with having AI players. Two different tech tree mechanisms are available in the custom options. The tech tree is based on unit advancements, but you can accelerate this process ('research a technology') by buying experience for individual units. Since AI is too stupid to buy experience, AI players can be allowed to gain quadruple killing xp. All aspects of the mod can be turned on or off individually by accessing custom options while setting up a game.
I'm grateful for feedback, regardless whether it concerns balancing, fun factor, or bugs.