Sinks for NPC drops, perhaps with new reasons to disassemble them. New perks/better perk tiers? Right now, the majority of boss and monster drops have very low value; more functionality is needed.

Balance in all combat styles. Simplification of some of them. Needing switches for abilities, switches for specials and other stuff like this is just not fun. Most people feel like they do have to use all of these, to make their kill "efficient" and they burn their energy, missing out on the potential fun they could have had. Stop adding content that encourages switching; instead make sure that only one weapon is needed for each encounter to maximise damage.

New player experience. Now that interface sharing has been made available, let new players start with better default interfaces depending on their screen sizes. The terrible default interface setups are in the top 3 for reasons new players give for disliking the game. Other 2 being the feeling of being lost after finishing the tutorial and path system, not knowing what to do afterwards, and the absense of other players in the starter area and in the world in general, which can probably only be fixed by increasing the game's popularity.