Been asking myself the same question. What facts do we have atm? First off, level 20 main and as someone wrote, its not gonna be as fast. Then 2 subclasses (probably 3 in the near future) to level 15. On top of that, theres farm for reputation so you can get better gear. Online pvp, also for rep/gear. Different modes to play. Then theres also 2 dlc's announced. Thats everything I can think of that one can spend time on. I'd say a few months at least :)