Just curious, is there any system that allows a group of people to sing together in real time?
I was just watching this ( https://youtu.be/z6QGqOagtJY ) and thought to myself… is this real??
Then I read this:
I don’t sing myself 
but I think realtime voice mixing would have applications in various other cases!
Hello, yes, it’s possible, but the approach depends on the type of music you’re doing. For drone-based works or chanting, network lag isn’t an issue, so jitsi meet or BBB could both be used. This can also work fine with free improv or anything where timing is open.
For exact timing, latency is always going to be an issue. One clever work around is the platform ninjam https://www.cockos.com/ninjam/, which requires some adjustment in how the choir would work, but could be useful for singing rounds (ie Row Row Row Your Boat), especially.
I wrote a few blog posts about online collaboration, mostly focused on jitsi meet, which you might find helpful https://www.fossbox.org.uk/?tag=network-music