Juli Clover, MacRumors:

At the current time, third-party music services like Spotify can only be streamed on the ‌‌HomePod‌‌ using AirPlay and an iPhone, iPad, or Mac. The new feature will presumably allow Spotify and other music services to be set as the default music service, letting users ask Siri to stream music from Spotify.

It’d be interesting to know if this new feature was directly driven as a legal strategy.