As previously announced, Google did not include their new Google Experience Launcher (GEL), that was introduced for the Nexus 5, in the just released factory images, such as for the Nexus 4.
Fortunately, because the new Launcher App is actually just a stub and all the functionality is now tied into the Google Search App, the Search App version that shipped in KitKat also makes GEL available for all devices running Android 4.1+. So, if you run KitKat, all the functionality is actually already there and you just need to install the correct interface (i.e. Launcher App). And even better, you don't even need to run KitKat for GEL. It can be installed on any device running Android 4.1+ (by installing/updating the Google Search App).
Fortunately, because the new Launcher App is actually just a stub and all the functionality is now tied into the Google Search App, the Search App version that shipped in KitKat also makes GEL available for all devices running Android 4.1+. So, if you run KitKat, all the functionality is actually already there and you just need to install the correct interface (i.e. Launcher App). And even better, you don't even need to run KitKat for GEL. It can be installed on any device running Android 4.1+ (by installing/updating the Google Search App).