As soon as it activates, Enlightenment is frequently frustrating for players: once they have used all their "normal" Action cards, don't realize they have not yet entered their buy phase due to having action-ified Treasures still left to play, so they start clicking on treasures. This reveals new cards, which makes the player's inevitable Undo requests problematic.
My request is that whenever Enlightenment is active during the player's Action phase, a small marker or token appears over each treasure card as a visual reminder that the card behavior has been altered. This could be a small circle that shows the face of the character on the Enlightenment card.
A good idea. We've tripped over that a few times and it is not a problem in friendly play, but sure is when playing ranked.