I've been thinking about this a lot lately, for one reason or another. It seems like most operating systems have followed the same method of representing data. While they have changed, and expanded, at the same time, they've stayed basically the same.
For me, I wish that there was an operating system that represented data in a more "realistic" way. Right now, we run through folders and directories, organized hierarchically. They're represented as text and icons. I'm not sure exactly how it would be laid out, but I almost wish there was something laid out more similarly to how I tend to organize things in my daily life. I remember physically in what location, in respect to other physical objects, I put something, or where something I want to interact with is. Why not have this in the way we represent data? Rather than organizing things into textual hierarchies, they could be in "sectors", similar to rooms in a house. You would browse through your files and applications like you walk through your house. Finding a text file would feel similar to getting a paper out of a file cabinet, locating and playing a game would feel like going to your shelf of games and picking one. It wouldn't be trying to exactly mimic a real life environment, but rather try to implement the same thought processes of daily activities into locating and using data. The "Desktop"/starting point would be like a map of the different, probably user defined, "sectors".
So what I've been wondering, is what features are really necessary in an OS? Not necessary in a strict sense, but things that most users wouldn't want to go without. What would be great to have that isn't really around yet? How could things that are around already be tweaked to be better?