Everyone has their own individual tastes e.g. the three examples you have provided are not my cup of tea. I prefer to keep the walls neutral and add treasures I love to express my personality. My personality is displayed in my entire room not just the walls.

I like the tiny shelves idea because that way you have more storage for your things.

I think, like you said, due to the fact that there's a larger space when it comes to the hotel lobbies is the reason as to why it works. I think that no matter what you put on the walls (whether it be concrete or marble) will result in tiles not working out. The industrial look tends to be exposed brickwork anyway, or cream or white colours so maybe that's an option you could look into. What did you end up doing?

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!