It doesn't even have to be very big. I mean it could start off by implementing cross class traits and further customization of character growth (you know the PVP ranking system is kinda similar to Merit points from XI...not like it isn't doable for existing abilities). That in and of itself would give the game enough complexity; however it would completely throw out the 'balance'.

But then they could always make content harder too. Outside of Binding Coil's gimmicky fights, the new dungeons so far have never been overly difficult or complex to beat. That to me is a little depressing in a way.