Yeah: it is maybe worth noting explicitly for people that the speed of sound is sufficiently slower than the speed of light that two people laying instruments on opposite sides of a small stage can actually, if they have pickup mics and headphones using software carefully designed to minimize latency, be reasonably far apart over the Internet and have the same experience (such as between a bunch of musicians living in San Francisco, or all in the same region of Los Angeles).

Even about two orders of magnitude further than that, based on the work done so far.

For instance, 22.5ms latency has been achieved at a distance of 900 miles (between the middle of Kentucky and Boston) with SoundJack and this setup:

Both port-forwarded, both using Fast Music Boxes, both on fiber internet connections. First user had an MXL770 XLR mic and an Audient EVO4 interface. Second user also had an XLR mic and an audio interface.

San Francisco is 7 miles wide.

I think you're underestimating the amount of latency that the human ear can detect. If the audio is as little as 10 ms out of sync, either way, someone will notice that.

Depends on what sound you are measuring. A single drum hit where one channel is delayed by 10ms is very audible. Would a violin and cello player have issues playing together if one was delayed by 10ms though? Could anyone hear that in the audio itself, or even detect it in their performance at all? That seems a very different thing.

Sound travels at ~1ft per ms in air so 10ms equivalent to being 10ft away. Sure, you notice the lag at that distance but it’s still possible. 30ms (or 30ft) is the point at which I would give up on trying to play rhythmic music well. That said 30ms latency is a lot of wiggle room where the speed of light is involved

People watch each other to synchronize. Problem with network latency is the visual latency isn't any better than aural latency, unlike on a stage.

And I think you are underestimating the speed of light ;P. The round-trip latency (twice my distance) from my apartment in Santa Barbara to servers I have in Nevada and Northern California is 20ms, making me the equivalent of like 11ft away from those places by sound. If I were communicating within San Francisco or Los Angeles I should trivially be able to hit 3ms round trip times.

In theory, maybe. In practice, you'll probably be limited to about 15ms round trip.

How does this impact large orchestras? Some of these musicians have got to be (way) over 10 m apart. Even 10 m at the speed of sound is almost 30 ms.

That is the role of a conductor. He hears the piece as it should be heard and is active participant in "tuning" it. My understanding is that he can slow down/speed up various performers to get them in sync.

Performers need to learn to ignore the rest and play their instrument while looking at the conductor.

That's why they rely on light in addition to sound: watching the conductor, watching each other.