The Drumset and Musescore: a different approach to compose, play, reuse your patterns.
Musescore is not only a score editor, since it gives you playback, can export audio file, handle the layout of scores. This starting point is needed to describe the following feature requests for the drumset, but useful to other goals and end-users (not only drummers). This starting point is needed to talk about usability and new ways to do things fast and better.
a) an acoustic drumset is a set of cymbals (hihat, ride, crash, china, splash) and drum shells (snare, bassdrum, toms, floortoms). You could play hihat open/closed, play your ride in many ways, but this is the most classic drumset (eg. cowbell is a percussion, should need a new score).
b) You could have different profiles of drumsets, usually designed around musical genres in the last century  or following some market standards (eg. by-pieces/size: bebop > fusion > standard > rock > metal). These profiles change the number and the size of cymbals and shells, changing playback too for a realistic feel.
c) a drumset - in whatever profile - should be played with 4 "voices" (2 arms, 2 legs). In a drumroll, have voice1 and voice2 could be translated into LRLL-RLRR-LRLL-RLRR (for paradiddle)
d) in a song, a drummer play some foundamental rhythmic patterns (repeated and dominant), add fills and other "colorful" things for a better performance.
Editing scores per-instrument in musescore is already available, but the drumset composer should have a better user-experience for his work, to do things fast reusing rhythmic patterns already made, new tools to create a pattern and test it with playback, write notes on a score.
1) The "Edit drumset..." menu control some aspects over notes, but nothing about your drumset and the available sound for playback. An drumset composer should select his kit around those describe above on point b) [bebop; fusion; standard; rock; metal]. This choice could add additional notes for the performer (eg. bebop kit), change the way to put notes on score (eg. with a bebop kit you don't have more than a 12"tom or 14"floortom, you should lowering the pitch of bassdrum since usually is small ~18", should open-up the sound on with unmuffled heads, change the cymbals' sound for playback). Take back to the intro, it's not only score editing.
1.1) [OPTIONAL] A drumset composer should have a way to create its own kit starting from those available/standard (eg. adding cymbals, effects, ect).
2) The "DRUM entry mode" should have a different approach in 3 steps:
2.1) a matrix-mode (ala hydrogen) to edit your rhythmic pattern and test it with playback. Obviously, you should handle only those percussions available for playback and described by your drumset kit of choice. With this matrix-mode editor you don't need anymore the "Drumroll editor...". This way should handle tuplets (eg. triplets for swing feel - take a look to hydrogen).
2.2) a way to save your patterns into a reusable library. You don't need to reinvent the wheel everytime. This concept could be exported to other instruments, but drumset and percussions are obviously the most exposed.
2.3) Export your rhythmic pattern in notes on your score. Usually a pattern could be around 1-2 measures, to be repeated a number of times. In this step you could select some styles for notes (eg. how stem should be, up/down - ask to lasconic for the french mode).
The composer could freely change and enhance further his work on score.
 for more info, take a look at "The Century Project" of Daniel Glass.