You don't need a Nexus 5 to take Android 4.4 KitKat for a test drive... you can now download some apks to get the new KitKat launcher running on other Android smartphones, like the Galaxy Note 2 in the video below. Full download/installation instructions here: Get Nexus 5 Android 4.4 KitKat Launcher on Your Phone (Video)
1. Download this zip file, which consists of three APK files. [mirror]
2. Extract the zip and place the APKs on your phone
3. Install PrebuiltGmsCore.apk
4. Install Velvet.apk
5. Install GoogleHome.apk
6. Press home button, select the launcher and enjoy!
Note: it probably won't work on all phones, so take caution.