I see a lot of cosmetic things being added. Maybe titles, tabards, transmog items. I could also see adding toys in there as well. Exp boost potions, but kind of pointless if they're doing bought level 90s.
I don't see them embracing a pay to win mentality in the near future. I could see them selling time saving items as well. Maybe a portal from draenor to stormwind or something along those lines.
Beyond that, I doubt we'll see anything to help out at max level, especially anything like gear/bonus rolls.