The Songshift app for iOS is used by lots of folks to synchronize playlists between multiple music streaming platforms. The app supports quite a few streaming services so check out their site.
As far as I can tell, this can be used to migrate playlists while changing services, but it can also be used to maintain playlists across multiple services longterm -- and share those playlists with friends on the services they use.
Some ways this might not work for you:
The source code (markdown) for this article can be found on GitHub.