I love the idea of customizing for this game and will certainly add the filled out blanks into my game. I'm not yet committed to any of several ideas, as I'd like to own the expansion first to avoid duplicating an effect already on a card I haven't seen. I did note from the Zee Garcia video review that the blank event cards did have the cross costs pre-printed on them. One was visibly a 1 cross and another was a 2 cross card (unknown/maybe three on the last?). This places minor limitations if one is trying for three balanced cost/reward ideas matching the print on the cards. Unfortunately I'll have to wait and see what fits the constraints.
An interesting new cost type is shown in the video on at least one new event: "1 cross per player in the game". Very creative and a good balancing tactic for the new type of "persistent effects" that last until the player's next turn.
Very impressed and I know this game is on my wish list.