i know the scratch team aren’t exactly fans of playlist projects, but in which case would one be acceptable?

What exactly do you mean by a “playlist project”?
If you are referring to a project where its main function is to play music, you could try incorporating buttons (and maybe even a “search” bar) so that you can play music without clicking “see inside”. Scratch is for coding, so I would recommend coding a music player, if that makes any sense. Kind of like this one.

Using copyrighted music as the main focus of the project isn't allowed (eg music sharing projects.) (However if its your own music its fine).

Using copyrighted music with something else as the focus (animation, art, game, etc) is fine but can get taken down if the OG music creator requests a DMCA takedown and sees your project (which is unlikely but has happened to GD projects and that one pac-man project).