This idea has been more or less confirmed by Square Enix. Right now all we know is that the developers stated an "advancement" type system was one of two different ideas they were talking about. Many on the forums have come to popularize the Final Fantasy tactics job advancement system, where upon reaching certain ranks/level combination's on different classes would open up "advanced classes".

However an official announcement confirming this was the path SE has decided to take, has not been made.