I myself have thought a lot about this too. I think business and first class by and large have seen developments, and are not really "problem" areas. The place where there is need for improvement is the coach class.

Unfortunately, things in this area are pretty much pared down to nothing as is. every inch has been utilized, and in many cases over utilized I don't think there is much that you can do right now to improve comfort, convenience, and safety without having to give up on a few areas. But with that in mind, I think that there is huge room for those airlines who would be willing to risk giving a little for reap rewards in the future. LED lighting is a good start - I think lighting can really enhance the cabin atmosphere. I think we have pared seats down a little too far - cuts now directly impact comfort and safety (we will not even get into those new offset seats!). In fact that might be one area of key improvement, Look at the design of high-end office chairs, and I think you might find some very efficient designs with high comfort there. I think that in the MP3 era the time has come to revamp in flight entertainment - why does my IFE for the seatback need this huge box under the seat, when I can store more programs, music, and video on my MP3 player that I can hold in the palm of my hand?