Levelling is very fast an easy in this game. Even currently you can do 90 to 100 in 3 days per job casually - less if you grind 90 Alliance raids. We probably have 2 to 2.5 years of this so if you are already all at 90 levelling is just a drop in the bucket of keeping entertained.

I'm pretty sure bonus XP is mostly designed to have you interact with the majority of the playerbase from various roulettes to keep them reasonably populated.