One thing I hope they improve is the artwork on the Ragnarok items.
They're OK in game, but when you see them in store, or in the inventory they look, sorry to say that, awful.
An aesthetic improvement overall of the game would be very welcomed, as well as an overhaul of the items. Not to make them overpowered, but fair and balanced.
A new mastery would be great.
Guns, to me, is a no go, mainly because of the thematic of the game. Ancient Mythology.