The Google Experience launcher isn't new, it's the Google Search app
It turns out that instead of breaking out the launcher, Google has folded its launcher into the Google Search app. The most obvious connection to prove this is the fact that Google Now has a dedicated page to the left of the default homescreen. Of course, the evidence piles up the more you dig. When searching, the results now offer direct links to open results in apps that are installed on your device. And, as Mr. Amadeo is wont to find, the Google Search APK from Android 4.4 contains assets that had been part of the 4.3 launcher; and, if you attempt to sideload the Android 4.4 GoogleHome.apk without also loading up the Android 4.4 Google Search app, the launcher simply won't work.
So, it looks like the Google Experience launcher will be coming to the Google Play Store, but maybe not in the way we thought. The Google Experience launcher could simply come as part of the Google Search app, along with Google Now updates. It's unclear as yet if the launcher additions will be pushed to older versions of Android, but it does look like the launcher has been inexorably tied to Google Search, which really isn't all that surprising given that this is Google we're talking about.
source: Ars Technica