Better custom key signatures
I brought this up on Reddit (https://www.reddit.com/r/Musescore/comments/mqikid/how_can_musescores_s…) as part of a more general observation about the state of microtonal composition in MuseScore, and the reception seemed positive enough for me to float the idea here.
MuseScore's support for custom key signatures is kinda sad. While it does let you create them by dragging and dropping accidentals onto a staff, it's entirely cosmetic - the key signature doesn't adapt to the clef in any way, there's no attempt to automatically position the accidentals horizontally (thus ensuring that a custom key signature is almost guaranteed to look amateurish and bad) and scripts cannot interrogate the current key signature to determine what the default accidental is for a given note. (While staves can tell you the current key signature, they do so by providing an integer representing the number of sharps/flats, which is fine for 12TET but meaningless as soon as you work with divisions of the octave which don't have a circle of fifths. (In 31TET, the key signature for C semisharp major has seven semisharp accidentals. The one for B semiflat major has five semisharp accidentals and two semiflat accidentals!)
Dorico is running circles around MuseScore by comparison with its concept of a tonality system; while I don't think it's unfair to relegate some of what it supports to scripts like the n-EDO retuner plugin, good support for custom key signatures matters to everyone, not just microtonalists.