They need to proceed with caution. Siri is universal and "play Madonna" is too generic of a command. Would it play from my music library, Spotify, find the movie on streaming services, etc? If you were actively using the app would you need Siris assistance at the expense of making Siri more difficult to use by requiring specifics system wide. "Hey Siri play Madonna in (insert app)".
The Devils in the details.
The best thing about Siri in my opinion is when she responds with an action. Ex Play Secret Earth...music plays. The worst thing is when she responds with another question ex. Play Secret Earth, "Which app would you like me to.....at that point I could have done the task faster manually. It drives me nuts that I need to specify mobile, work, iPhone etc when making a call SOMETIMES....