A 4th Pro Tour has been returned to the 2014 Premier Event calendar, as announced at Pro Tour Gatecrash:
It’s happening: we’re adding a 4th Pro Tour next year! Announcement will be posted on DailyMTG on Monday
— Helene Bergeot (@HeleneBergeot) February 16, 2013
Previously, the Premier Event calendar had featured five Pro Tours, including the World Championships. Worlds has been replaced by the World Magic Cup and the Players Championship, but until now the 4th Pro Tour had no replacement.