I think an equal amount of people would leave. The game relies on 12 elements. Think supernovas, black holes, and quantum towers. Also the layout would have to be redesigned to fit a 13th element. Sure, 10-15 new cards would be awesome, and I think it would get people active. However, you could simply announce that a new card for every element was being created, have competitions, ect. It would be much easier.