Being such a big space, maybe a series of framed photos would be nice. The frames should be somewhat cohesive I would think, as in black or dark wood, but certainly don't all have to match. Doing that in my own home; it's a work in progress!

I think a series of three squares moving up the wall could work. Cut out pieces of paper to tape up and try it out. Updating the sconce glass to something more substantial and geometric would look nice also.

one or two of something long and narrow to match the shape of the window by the door. What is your style/interests? It could be a couple of boat oars, long chinese water colors, tapestries, etc....