I just got a notice from Volaris that, beginning for flights purchased after March 1, all International flights will be charged for the first and subsequent CHECKED baggage. 2 small cabin bags still allowed free (but watch their size limitations). Domestic flights still have 1 free checked bag.
Volaris's pitch: This new Baggage Policy gives you the option to choose if you wish to fly with a checked bag or not, so you can get the best fares to travel more.