May I suggest that you look up the NCC Volume 2 which specifies the safety design parameters for stairs and balustrades. Any new work done on stairs and balustrades must comply with the code. You need to look up sections 3.9.1 and 3.9.2 In summary, whatever method you look to you can't be able to pass a 125mm sphere through any part of the stair or balustrade. It also specifies the design parameters for wire balustrades to achieve the 125mm sphere rule. The design challenges for stairs are significant if you want the open back tread look. The easiest way is to install a block on the underside of the tread level with the back edge of the tread below. This way you can still have an open tread and achieve compliance. The harder problem occurs when using a wire balustrade and the resolving the gap that occurs between the treads and the lowest wire. I have seen several installations of late where the 125mm rule was very clearly not achieved. One was a very recent build and I'm still not sure how it passed the final inspection. The images from Miami Stainless show how this can be achieved. Clearly the best and most secure is the glass balustrade and the vertical bar balustrade. Good luck!

You could add a chaise lounge or a comfy chair and table for a reading nook or an office area if you need one, a computer area but whatever you do don't over clutter it keep it sleek and sexy and or a comfy chair as suggested with a little side table for reading, I also like the idea of a place to put coats, shoes etc if you must enclose it. Maybe even a small wine bar? with a couple of stools. I decided to google is and will give you a link to many pics to give you more choices. https://www.google.com.au/search?q=pics+of+what+to+do+with+space+behind+floating+stairs&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjFy-n9p4vZAhUEF5QKHSvhAOMQ7AkISg&biw=1280&bih=893

I think with clever design you can have both. Consider glazed doors, and glazing around the stairs. Why don't you get your architect to model both options in 3D so you can see the options? Best of luck with your considerations, Dr Retro of Dr Retro House Calls/Dr Retro Virtual Visits

Another option instead of a light well is to have a glass floor section in the ground floor just above were the stairs lands. and open the wall in the sitting room/use steps hanging in a wire. so there is plenty of light coming in one side of stairs plus light above the landing area. this brings some cool features to the house, which i am already thinking to have a glass floor section somewhere and a mesh floor section somewhere probably in the first floor above entry. Light is not an issue anymore again the big question is when you enter do you want to see the stairs going up or down. Hmm.. tough decision to make