I left the game some time ago and came back to level up some of my other characters (I have one Lvl 55 character), as it had 12x XP on class missions. This was a great way to get me back and I believe you should keep some sort of subscriber process to 12x XP. Even if only for additional characters after you hit the level cap (then 55, soon 60 ).
It means I can do the class mission on my other characters without the need to rank up the xp doing the side quests that I have already done. It's a great way to get subscribers as well, offering it as 12x XP all the time on class missions.
Please!!!!