I've always liked the ability to modify the piano brace in Finale (especially since the default looks too much like a seagull). I would like the capability to modify brackets the same way. One reason for wanting this is just to be able to. The other reason is because resizing the staff height or page size makes the bracket a bit too thin than desired. For example, when doing quartet music at .26" or .25" staff size in Finale, the bracket is so thin in comparison to traditionally engraved music that it makes the music look smaller than it actually is. Being able to control the shape and thickness of all braces and brackets would be nice, I think.
Also, I would like to see the option of being able to save/load only piano brace/bracket settings without affecting other document settings. If this is already possible, which library type saves it?