Above 8', you could just leave it blank, however, if blank bothers you:

https://www.google.com/search?q=pressed+metal+wall+art+flock+of+birds&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjimJfG1tvkAhVnUN8KHRMHAY0Q_AUIEigC&biw=1328&bih=617#spf=1568854530257

https://www.google.com/search?biw=1328&bih=617&tbm=isch&sa=1&ei=ftKCXY6kJNS40PEP_NuggA0&q=pressed+metal+wall++sun+or+stars&oq=pressed+metal+wall++sun+or+stars&gs_l=img.3...22109.26665..26853...0.0..0.96.957.14......0....1..gws-wiz-img.......0j0i67j0i8i30j0i24j0i10i24.H3VjXJtH8ng&ved=0ahUKEwiO25CD19vkAhVUHDQIHfwtCNAQ4dUDCAY&uact=5#spf=1568854683513

Above the stairwell, a family picture could fit in that niche.

I like that idea. It’s subtle yet fills the space a bit.

For the dining room leave it blank. Only decorate at eye level. However, I think a new, grander chandelier (hung at proper height) would look really great there.

For the staircase, I agree on closing up the niche and hanging some nice artwork or doing a gallery wall.

Yes, I have been searching for the perfect chandelier. I can’t wait because I know that it will make a huge difference.
Thanks for the advice. I might just leave the large wall alone.