Yes, we finally installed a mirror on the empty wall!
Initially, we planned to hang a mirror at dining area which will be a feature wall as well. Anyway, after considering few factors and some feng shui tips (husband-wife-cat-fights-included) we decided to put a mirror on an empty wall by the stairs. Turns out it was the best decision ever! It does make our home looks brighter and bigger.
Our mirror is from HEMNES series Ikea.