It's worth noting there were at least 3 other de-facto standards for USB to TRRS: https://qph.cf2.quoracdn.net/main-qimg-d6cc903458ff8fcfa304d...

One problem with using TRRS for USB is that Vbus can be short-circuited while plugging and unplugging; the clones of the 2nd generation Shuffle tended to use a regular mini-USB instead, which offers the advantage that it can be charged while listening: http://tarkus-notes.com/en/chinese-mp3-player-ipod-shuffle-c...