Hit and Expertise turns into Crit/Haste/Mastery on 550 PvP gear.
Check wowdb (Wod Beta) now and have a look at the stat changes on your PvP gear.
Example:
I have a ww monk.
Stat priority: Crit>Haste>Mastery
Right now there is one waist with Crit+Mastery and one with Hit+Haste. During 5.4 I had the former one equipped.
In 6.0, though, the latter waist will have Crit+Haste on it. That means come 6.0 I will go with the latter.
Of course you will be able to purchase all 550 PvP gear with honor with 6.0, but seeing that all your current conquest points AND honor points are being converted into gold, I'd advise you to buy the 6.0 BiS gear now.
Hope I could save you some trouble
cheers