Real time notation for small groups, so they can work out exercises (ie, four-part harmony, variations on melodies, harmonization) and also get comments from others. Breaking a large class into small groups is very effective for remote teaching in music theory.
As someone who has been using MuseScore daily for the past decade in my teaching, my deepest respect to the developers and community, you have built a piece of software with real impact that challenges proprietary (and very expensive) alternatives. Kudos to everyone involved in this life-changing project.
Looking ahead, it would be rad if some form of real-time collab could happen with MuseScore, either with the software or MuseScore.com embed.
I miss uploading images and PDFs that I can "lock" and write on top. Ziteboard does it, but it is expensive and also when someone zooms everyone is zoomed, which kind of sucks. Jamboard is also bad at writing on background images. We do need a good whiteboard app with a simple share indeed for classes.
Those are all good ideas, I am mostly going the fully offline route, however some teachers lack time (too many classes), experience or equipments to produce good content.
VoIP is new to me, I will look at that. I also found that Microsoft Teams has policy settings to limit bitrates for specific users, so that might be also an option to limit bandwidth for students with data limits (between 3-6Gb/month in basic plans around here).