Basically what this does is that it lets iOS users choose from a variety of new themes that they can use with their phones. These will be paid themes of course but if you think that the customization is worth the money, then why not? SwiftKey claims that there will be a dozen new themes, one of which will be an animated theme, and five of which were not in the beta.
SwiftKey believes that the theme store for iOS will be a huge success. It was apparently one of the top user requests since the app was launched, and its Android counterpart has seen more than 26 million themes downloaded since its inception, so presumably that level of success should continue with the iOS version.
Apart from the introduction of a theme store, the update to the app will also bring about performance improvements. The update should be live and available for download so head on over to the iTunes App Store to get your hands on it.