And that’s just for an idealized communication network. A real world use case would have a lot more latency introduced by routing/switching, and all of the typical quality issues you’d expect from ISPs. I used to live within line of sight of the data centre that hosted an online video game that I played, and the lower bound of my ping was about 15ms, it was usually in the 20s. Those factors are why something like this is unlikely to ever provide a high quality experience over even relatively short distances. I’ve just always found it interesting how quickly you start to run into issues with the speed of light when you’re trying to optimize for network latency.
(And no: you are wrong about round trip. If you care about round trip time then 3ms of round trip by sound is so close that the violin player is going to be elbowing the singer. Sound is fundamentally slow, and you need to just accept that.)
Also, the reason you'd care about round trip time, is if you needed mixing or processing to be done to musician foldback (I never mentioned 3ms being an issue btw). The mixing and processing of sound is prior to being sent to foldback monitors is a completely standard process in just about all live and studio sound engineering. Latency is a very important consideration for sound engineers, and it's why in situations like stadium performances, the only sounds that matters to a musician on stage, is the sound coming out of the foldback monitors directly in front of them. I'm getting a rather strong impression that you don't know much about what actually goes into sound engineering.
FWIW, when I asked my professional musician ex about all of this (which was before I read this comment of yours here) she also mentioned monitors, but it was because she claimed a core consideration for her with respect to distance in a performance was volume of her instrument drowning out her playing companions (and when I pushed into that she said if the acoustics were bad enough they would use monitors). She also told me that people she knew were already using software to play with each other over the Internet. If nothing else, I feel like "proof by counter example" should win here vs. your statement that this is just somehow impossible? As others have pointed out in this thread, the SoundJack people exist and claim to do this (whether or not you believe they have users: my ex apparently knows of users, though I don't know if they are using the same software).
I honestly just don't think you are truly appreciating that light is almost a million times faster than sound.