The developer working on integrating network display functionality into GNOME Shell shared short video clip to the GNOME sub-reddit […] the feature adds a “screencast” button to the row of actions in the Quick Settings menu. Clicking this opens a modal picker where the user can select any Miracast or Chromecast compatible displays on the network.
Currently, you’ll need to install google chrome in order to cast your desktop to a chromecast / smart tv. With this update we’ll be able to cast the desktop without needing to install chrome first.