1. A real full screen mode. Neither Word nor Scrivener do this properly, but OmmWriter gets it perfect. 2. Speaking of OmmWriter, I love that you can turn on tikky-takky keyboard sounds and have built-in background noise/music. Anything that minimizes the number of times I have to go anywhere else.
3. A floating design/layout/type widget for fullscreen mode, so I don't have to exit out of fullscreen to add a new page, center a line, or do anything beyond bold and italics. Being able to toggle the widget with two keys so it can stay hidden as needed would be even better.
...apparently I just want fullscreen mode to be more immersive, hmm.