Have you heard of Soulseek? It's an active p2p music sharing platform.
replyHow would the plausible deniability piece work? If you stream some bytes to someone else, you can't deny doing it. Unless you imagine this working over Tor, idk what the performance of Tor is these days but I never thought it could support such an application.
replyMusic is relatively small. Tor is totally capable of hosting zlibrary without bandwidth restrictions getting in the way.
replyBy plausible deniability I simply meant adopting a similar approach that Stremio has, to keep it on the good side of App Store approval processes. The app itself only allows for creative commons content by default, but with the right incantations it can host anything.
Stremio and other apps like Fusion have gone up and been (reasonably quickly) taken down off the App Store though.
replyNot really "on the good side" when your main distribution method is "add this app to your account within the first 1-2 weeks of it being in the App Store or never again", or sideloading.