Hi! I love Musescore it's amazing!
That being said, I loved something from cakewalk that isn't seemingly possible in Musescore - yet.
Arpeggiators are rudimentary programs that change chords into arpeggiated notes.
I feel that although it may sound out of the scope of a score-oriented software, it would greatly help save time in writing certain melodies.
As for the bank of possible arpeggios, it could be a simple musescore sheet from which we can pick a measure and even add to.