Hardcap for now seems to be lv20, but there are ways to go beyond that. Some legendary gear have this stat called "Light", and this stat will push your level up depending on the value, or so i have understood. So lets say you're level 20, and you find this fine piece of loot, gloves for example. These gloves have a stat Light+2, this means it will raise your level from 20 to 22 when you equip it. This was all in the alpha already ;) You could examine these items that had that light stat and it said something along those lines i explained. As for the ultimate maximum level with these light stats, we don't know yet, could be 40, could be 50, could even be 100, we don't know how high those will take us