I don’t foresee us implementing anything like this in the near future, sorry for the bad news! Our position has always been that we want to let users like you bring your own form of entertainment to training. Because implementing this would mean linking the TR app to a music player, we’d effectively be picking a favorite, and if you use a different platform you’d be left out. As you can probably imagine, adding cross-compatibility to multiple platforms would be a major undertaking, and we ultimately want to focus our development resources on internal TR features that will make you faster.
For now, my best recommendation is to use a standalone music player with your favorite playlist to hopefully motivate you enough to get to the end of an interval.
For a little more information, take a look at Bryce’s response to a question about integrating Spotify: