Idea: Save quest XP for next expansion.

While waiting for a queue to pop, I was running some sidequests for gil, and noticed that they also awarded significant XP, which was going to waste, since I was already at max level.

So, why not let players at max level still collect XP, but "bank" it to be applied immediately at the start of the next expansion, either all at once, or spread out over several weeks. This would make 70-level content a bit more valuable, and could give you a good head start going into the next EXP.
Also, there would be more players out in the world running these instead of just hanging around in the cities.