For all we know it's just Google activating the device to ensure it wasn't stolen and reflashed with another OS. Apple requires a device to be activated before it's usable.
The problem with Spotify's Local Files feature is that the music you add cannot be added to Liked Songs. They must be in a playlist in order to be synced across.
As someone who listens to their music by just tapping shuffle on Liked Songs, this is a no-go.
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