A fun part of the game before it begins is picking a civilization/leader based on their traits. How about adding this into the gameplay instead? All civs/leaders could be vanilla with no advantages. There could be a tech tree and you can pick your abilities as you progress, maybe every once every era. It could even be done indirectly, where you don't choose your traits, but they are assigned to you by decisions you make in the game or by how you progress through the tech tree. Say if you pick seafaring technology with your first tech advancement, you get a trait bonus to match.