Both ideas are great. I never store my shoes in bedroom wardrobes. I have an inbuilt wardrobe in the laundry and two sections are for shoe storage. As soon as everyone comes home the shoes are taken off and left in the laundry so they can aerate and then they get put away in their clear plastic labelled boxes or the hanging shoe shelves (for everyday shoes eg sneakers, work shoes etc.)

Agree with all above. First think what you need the extra space for - you have lots of options. Also remember it is a walk through, so a 'public' space. If used as a study would be best if not too messy or private.

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