Comment 39 for bug 938180

There is no opting out of making a moral decision here. Artificially disabling features requires code inside Mixxx that deactivates the feature. An external plugin cannot do this by itself. So either Mixxx condones this or it does not. If the Mixxx community decides that it condones violating the user's freedom to use the program for any purpose, then I can no longer trust the Mixxx community. Mixxx would no longer be free software and would therefore be worthless to me, so I would fork it.

Hypothetically there could be a plugin API for external audio sources that does not impose artificial restrictions on Mixxx's functionality, but there would be no practical, legal use case for this. If someone wanted to develop a plugin that violated the terms of service of some streaming API, then it would be up to the plugin developer to bear the potential legal consequences. If someone wants to do this as a deliberate act of civil disobedience, that is up to them. Most likely the streaming company would simply revoke the API key rather than bother with legal action (unless the developer tried to get new API keys or otherwise circumvent the ban), in which case all the effort spent developing the plugin and the plugin interface would be wasted.

Let's keep in mind that a plugin API would be a big maintenance burden. It would require interfaces both for sending audio into Mixxx and ways to interact with Mixxx's GUI. FWIW Mixxx already has an interface for receiving audio from any external sources (the auxiliary inputs).