@skobkin @geerlingguy easy enough to work around on android as you can restrict an app to only use wifi & not mobile data, but you need a player that can handle that without crashing and you'd still need a unified format for play-lists (eg .m3u files) that you can dump into a cloud-synced location.

Eg: Say I usually use Rhythbox on my Linux Desktop, I'd still need to figure out how to export the files with a play-list.... Hmm maybe I should look more into nextcloud clients...