Is libspotify available as a plugin for any cross-platform SDK? I'm talking about a native plugin for mobile SDKs like Phonegap, Gideros Mobile, Corona, Intel XDK, Marmalade or similar.
libspotify is a C library compiled for various targets (Mac, Windows, iOS, Android and various Linux variants), so there's no single cross-platform build.
However, it should be possible to create a wrapper around libspotify in these SDKs and deploy them along with the pre-built binaries to the platforms libspotify supports. There's nothing official like this, though.