This would be very useful for composing: A side panel (detachable, collapsable) containing customizable music fragments. A music fragment can be a musical motif, a phrase etc.
The user can drag a single music fragment from this panel to the score and drop it on a desired position, where it will erase any existing notes for the length of the inserted fragment. When the CTRL key is pressed while dropping the music fragment, then it will be added as an additional voice to the existing notes.
The user can also drag a selected portion from the score to the side panel to add it to the current list of music fragments. After that a dialog opens where different properties of the inserted music fragment can be optionally customized: Keywords, Category, Instrument.
The user can load different custom categorized lists in the side panel, for example: Classical, Rock, etc.
The list of the music fragments can be sorted or grouped by: Keyword, length.
This would be very useful!