I think we need to try some opportunities for differentiating civs. I recently made a mod change gameplay as a whole, but a more conservative approach would be to only differentiate a few factions. Also since gameplay mainly stays the same, people do not need to adapt as much to the new settings to enjoy the game.
I differentiated the following factions:
Athenians: Can now reasearch economic technologies for 50% less metal. Coupled with the extra metal mining speed this encourages play
It allows you to use things you would normally not use and it gives a little extra benefit to unlocking these buildings/p2. Also it allows you to vary your playstyle a little. The Gallic, Roman or Ptolemaic team bonusses don't encourage varying your playstyle.
The idea with the theatres was also basically a way to research city phase faster. It only affects those who have access to a certain unit, but the Kushite team bonusĀ also only benefits those factions only with access to elephants.