I know accessibility for low vision users was mentioned, but I wonder, with all these changes, whether version 4 will be accessible to screen reader users, and if so, whether any major features will nevertheless remain inaccessible.

We're using the framework my team on MuseScore Studio created for the UI in Audacity. This allows us to port over the significant amount of screen reader support we built over there too.

We'll need to spend time making sure it's applying correctly to every corner of the app - but when it's done, the app will be far more broadly supported than V3.

I would guess accessibility will be similar to the current version of MuseScore since the same company (Muse Group) is leading both open source projects. So maybe look at MuseScore.

https://en.m.wikipedia.org/wiki/Muse_Group

Nice update — hope it rolls out smoothly.