Currently notifications about laps/pace etc get played on the bt headset during music playback. The watch does mute the music first, then plays notification and then unmutes the music again. This is a very weird experience when you are nicely stomping away on some beats, having a great pace guided by the music. Then all of a sudden, no sound.. then a notification .. silent again.. music is back.
It would be a lot better if the music would continue to play, but at a lower volume. Mix the notification over the music, like what for example happens when you use your phone with Runkeeper + audio stats. So music would go to 40%, notification at 100%. After notification the music would go back to 100%. (Smoothly please!)