Three General Features I'd Love to See in User Interfaces
1. Guaranteed performance levels, so that the system never locks the user out due to thrashing, virtual memory swapping, or cpu overload. For example, have the system always reserve (say) 10% of CPU exclusively for user interaction, so that the UI will always be responsive.
2. A "Wikipedia" like approach for collaborative user interface design, so that open source software developers can actually get real designers into the game. Make it so that it is possible to have a clean separation from back-end and front-end, and that anyone can go in and offer feedback and alternative designs.
3. Make it so that I can "patch" my own UI to fix bugs. For example, Intuit Quickbooks maps Ctrl-A to opening all accounts, instead of selecting all text like every other system out there. I still make this mistake despite using the software for almost two years. Alternatively, make it easy to send the patch to the developers, so that they can apply it and fix it in their next release.