This is the current look - it will be being repaired at some point from the many earthquakes we have had over the last two years and it is currently a very dark room. I would like to warm it up somehow. Suggestions? I did consider, white panelling 1/3 way up the wall and a collection of mirrors to reflect the light in.

Did you end up painting the ceiling all the same? That's what I would've done!

Joanna Gains style is fun! What you choose for lighting and surfaces will determine the amount of reflective light in your stairway. The Architect is right in what he is suggesting "a decorative wall" could bring more light into the space. I believe you could apply this on principle....for example you could do a feature "Architectural Mirror"or lots of mirrors on the wall in the right position to reflect light in "Joanna Gain style" then in the same style add an eye catching pendant or wall lights depending on what is best functionally. Remember what you use on the ceiling & walls is important too every surface counts for your situation. Try a satin finish with a cool white like Dulux "St Clair Quarter" or Resene "Black White" Maybe Nancy's suggestions of a skylight is an option for your situation if it allows ? Natural Light is always great. Heres some inspiration...All the best!

Textured linen or with a subtle print wont date. Feature walls make a room smaller as they jump out ar you. Wouldnt recommend. Get some interesting art or craft. Pick up colour with accesories