Would it be worth designating a permanent room for helping people test audio and get setup? Rather than bursting into a room feedback squealing all over the place people could go there first and help each other with the “Am I coming through?” “Can you hear me?” questions.
Doesn't need to be recorded or anything just a safe space for people wanting to configure their gear and get pointers on how this all works.
Have heard a lot of people in rooms checking in and getting weirded out by the “massive delay” or laughing at the “poor latency” without grasping the concept and leaving.
Maybe on second thoughts the idea is not to cater for these people. I dunno though, I'd like for people to have a positive experience during these weird times.
One thing that I think also might be useful is a spoken word metronome. As a lot of times also I have heard drummers completely playing to the BPM but starting mid sequence and it getting weird. So if there was a 1, 2, 3 … etc to show where you are in the interval it might help. Optional of course.