How would people feel about the Age cards if they were tweaked a bit? Something along the lines of "Everyone can use 3 upped light cards."
This still has a similar feel to the original Age cards, without being gamebreakingly unbalanced. Here people could use it if they wanted, but the disadvantage for not using it is minor.
Edit: As long as we're listing the cards that give an advantage to specific teams over others, Burst of Color is pretty dang biased towards team underworld.
I'd be much happier if it didn't arbitrarily punish people because their Element happens to not synergize well with light (i.e. they have no Light cards in the vault.)
Something like:
Age of Light -- Players who win a game using a :lightmark may salvage an additional 3 cards. Players who lose a game using a :lightmark discard 3 fewer cards.
That way, you have to balance the fact that everyone will predict you will play whatever

-related strategy you can versus the fact that playing to counter that strategy will actually be more likely to win you the game. It gives the
flavor of an Age of Light while providing a relatively
balanced and
interesting mechanic.