Gorilla arm would prevent people from using that kind of system to replace mouse and keyboard, but I don't see why it could not work for some applications. I can think of several use cases where I would like a UI that does not require me to touch the hardware (think cooking or watching videos in the bath tub).
Yes using 2d displays in minority report was a huge mistake, but imagine it in 3d.
Also that doesn't mean that you will have to keep your arms out before your eyes. Ideally you don't have to sit before your computer the whole day and use only a keyboard and a mouse, when you can have so much more freedom.
Think of opening a book, ironing, or placing lego blocks etc.