A few improvements to Papers that would be great to see.
1. It would be great if all select items could be modified using the text formatting options. For example, command-A all items then change the font. Right now you must select the text to change text format. It would be great if you could select just the outline object.
2. Sync between systems (I believe this has already been mentioned). I'm using Papers quite a bit in my prep. between two computers so sync would be huge benefit. Right now I'm doing it manually.
3. It would be great if you could select individual elements to include per outline object (summary, content, notes, etc). Or, if one of those is blank the line disappears (rather than currently it inserts a blank line in your document).
4. I've also noticed that in order to get all the text on a printed page the page margins must be less than 1.0 inches. Maybe this is my printer...