This is not a bug!
Quest has never permitted audio sources on avatars.
It was a bug that some users could modify their SDK to work around limits and have audio on Quest avatars. We fixed this bug.
This isn’t a bug report thread, please post to our Bug report forum! (I have also experienced that bug, but rarely. Hit “respawn” and then recalibrate your FBT)
No news on this front.
They’re laggy?? News to me. 
No plans at the moment, but cool idea! While MOD is cool, MIDI is a bit more widespread, so I imagine that’s why @momothemonster went for that first.