When you are on hold with Apple (let’s face it, it happens), Apple should play your Beats playlist to you. It shouldn’t be that hard to set up. Apple knows your phone numbers and uses caller ID already. They can equate that with your user account. From there they know things like your music in iTunes and theoretically that will tie into Beats.
It would be even better if you could create a playlist in iTunes called “Hold Music” so you could specifically set your own hold music.