I could see where the graphics might need tightened up, possibly on level 3.
Polish can and probably will be improved, especially on skills and effects, but this will likely be opportunistic, rather than predictable.
I don't think we'll be seeing upscaling to higher resolution pixel art anytime soon. New monsters (playable and otherwise) and worlds are the graphic additions we're most likely to get to.
As far as reskinning anything, moving to 3d, or other from-scratch approaches, you can bet we'll just make a new game, first.