For me, a more sophisticated character customization system. It's amazing how sparse WoW's system is when in-depth customization is a standardized and default feature of all other f2p mmo's present and future. I mean, for $15 a month it should be a given. Just really sad to see how slow Blizz is when it comes to implementing certain features that people would think would be included when the game first came out. Took 4 expansions before AoE looting was added and it's not something as pivotal as inventing the wheel.