https://en.m.wikipedia.org/wiki/Comparison_of_online_music_lockers

Many were sued into oblivion, and of the big names, only Apple, which negotiated with the record labels before launching the feature, still has one going.

I already wasn't getting good vibes from your comments, but the use of "FUD" is a surefire way to lose credibility.

Music locker services are frequenly targeted and taken down, as GlitterInfection mentioned. There's multiple cases on the Wikipedia page.

There is a jump between hosting and sharing, but that jump is very small. Share it with 1 other person, and you have made unauthorised copies of the licensed material, and are therefore acting against the law. That's not FUD, that's been reality for the past few decades.

Whether or not the illegal sharing of licensed material is done via a generic website, a federated service of even carrier pidgeon doesn't matter, an unlicensed copy is an illegal copy. Rightsholders have pleny of avenues to force a takedown against specific instances. And if they can successfully argue that the primary purpose of this software is piracy, they may even have enough legal arguments to force a takedown of the sourcecode.

Of course, the main question is whether rightsholders will bother with this as long as it remains small-scale. Legal costs would likely outweigh the missed income. But that doesn't actually shield you from legal liability.