This has been confirmed on Skype’s support page where they announced that Skype Insiders will be the first to take the feature for a spin. “The Skype Spotify Add-in makes it even easier to share a preview of your favorite songs with your friends and family. We will be rolling this out gradually to all Skype Insiders in the United States on Skype (version 8). We will also be rolling it out to all Insiders around the world very soon.”
As with Spotify’s integration in other apps, the integration in Skype more or less does the same thing. Users can search for songs within the app, and when they’re done they can play it and share a preview of it with the contact that they are chatting with. However as Skype notes, not all songs will have a shareable preview and songs that do will be marked by an icon.
While Skype does not seem to explicitly mention this, we can only assume that you will also need a Spotify account if you want to take advantage of this feature. It is unclear if this feature is only available to Spotify Premium customers or if it will be available to all.