been waiting forever for Spotify integration (well 6months as a TEsla owner and I had read the Electek blog that it was coming soon, back in Sep '16). I bought slacker premium because kids wanted instant gratification - the song they want to play needs to play, simple. So this weekend, I told my son (11yrs) to move all playlists from spotify to Slacker so I don't need to pay spotify monthly - and he can get 2-months of spotify subscription as reward. He started on it for an hour, with multiple windows, faster search, drag and drop etc. He then gave up. did google search and said, Tesla will support spotify soon - and stopped the migration. I didn't tell him - Tesla's "soon" has time-bending logic that may keep stretching.
He might get back to the migration next weekend...we will see. Hate it that Slacker (or any other competitive streamer) doesn't have a "transfer your playlists" tool to make it easier to woo subscribers.
Do you have trouble getting any song you want to play on demand with the default Slacker? I've never had it fail to find the song I want when I request it with voice command. The only thing I can't do is immediately play the song again, but after a short period I can request it again.