My vision on the bonus tracks on the third disc would include the unreleased *We Got tThe Beat* cover by Rachel Platten, maybe one or two demos for *We Got This Together* and *Open Up Your Eyes*, the unused score for the original prologue cut from the final film, and (perhaps) three songs from the Rainbow Roadtrip special that shared almost the same animation style from the film.
It could be settled for the film's 10th anniversary in 2027, but we won't know until it's officially announced.