Trills on unpitched percussion
https://musescore.org/en/node/141936 is a discussion about trills not being played properly on unpitched percussion. While the discussion refers to 2.0.2 it also applies to 2.0.3. Though the snare drum rarely has a trill on it to indicate a roll, many other unpitched percussion do use this as standard notation. If the trill were to be simply passed to the 3 line single note tremolo it would reproduce the most common sound of a roll on an unpitched drum. The 4 line percussion tremolo just sounds very bad in anything but a very slow piece of music.