Currently, Muky uses only Apple Music's API, but I'm working on Spotify integration. Users will choose their preferred service during setup, with playlists tied to that service. Switching services will require new playlists. This approach, similar to Sonos, ensures API compliance and user consistency. I'm hopeful it will pass Spotify's app review when ready.
Ah I see, that's a good solution. It's a shame it can't be mixed, maybe not so interesting for services where the offerings are so similar like these two, but e.g. Spotify + YouTube would be nice.
I have heard (from the developer forums) that review time is awful since they became stricter on the requirements and the dev support team seems to have disappeared. Be sure to factor that in and good luck!
