I look the most forward to the wardrobe if I may be honest. Can't wait to have all the gear I gathered on various chars to be available for all my characters. The bad part is that I'm actually hoarding even more at this moment.
Secondly, the artifacts. I've leveled every class so far on my mainserver to maximum level just so they can have the artifact. This does ties in with the changes in playstyle.
I've never been much into PvP, but what I know about the new system now, makes me want to step into that part of the game more.
It's a promising expansion, let's hope they can live up to