Just to make clear, there are two different plugins being discussed here which have similar names:

Plugin Used on the WCEU 2017 PWA
Name: WordPress PWA (aka Frontity)
WordPress.org: https://wordpress.org/plugins/wp-pwa/
GitHub: https://github.com/frontity/wp-plugin

Core Feature Plugin
Name: PWA
WordPress.org: https://wordpress.org/plugins/pwa/
GitHub: https://github.com/xwp/pwa-wp/

The latter PWA plugin hasn't yet been formally proposed as a feature plugin, but that is the intention after WordPress 5.0 is released. Also, this PWA feature plugin is intended to introduce new core APIs which themes and plugins can use to implement PWA features. Activating the plugin will not turn a site into a PWA automatically. It is intended that other plugins and themes (e.g. Frontity) can leverage the core capabilities to provide the desired PWA experiences (e.g. offline reading, app shell, notifications, etc).