Apparently this was revealed over the weekend on a SWTOR livestream. 12x experience is returning as "Epic Story Mission Bonus" on May 4th, and stay for the foreseeable future. SWTOR class missions will have 12x experience associated with them forsubscribers. This will enable a Level 1 character to reach Level 55 (uncertain if it will apply to latest content which is 55 - 60) to level strictly through the class story. There will be an item that you can use to turn off the bonus.