JRiver might risk legal problems if we helped others create software that circumvented the agreements that the services have with the record labels.
I don't think this would actually be an issue, so long as the system implemented was general purpose. You'd be making a system that would allow end-users (third parties) to write a plugin that would enable this kind of integration (which could be used for
any kind of streaming service that offers an API, or maybe even other stuff too).
Then, it would depend on some nice guy actually writing the freeware plugin. I don't see how JRiver could be liable for the actions of a third party using your API. And, Spotify DOES allow freeware applications to plug into their API, just not commercial applications, so the third-party developer wouldn't be doing anything "wrong". They're writing freeware code that bridges between the Spotify API and the JRiver (hypothetical) plugin API. How is that different than writing a freeware iOS app that uses the Spotify API (bridges between the iOS API and the Spotify API)? Or any other conceivable purpose for the Spotify API? They're
all going to be a bridge between commercial API over here and Spotify API over there.
Worst case, I could see this third-party developer getting hosed if Spotify decided that wasn't cool, and they yank the API key.
The bigger issue is who is going to be this nice guy, and how nightmarish would it be for JRiver to develop an API that would allow plugins to work that way.