Wind of Change

I agree with Marek; random secondary skills will probably create more imbalance. And the point of building them becomes irrelevant. When playing with a Fortress, there's a very powerful boost in the form of leveling up support units, and also the ability to "correct" a promising main unit if it's not leveling up as intended when it was chosen. But the cost should be justified because 5000 for the building + 2000 for choosing the element is still quite cheap, especially for the mid-game and later, where utopias appear and trade artifacts become available at the merchant. Perhaps this is the most "non-barbarian" change, in my opinion.