Hey there! I recently extracted the Google Keyboard from my friend's N5 which was running on the Dev preview. I have tried it on various phones which were on 4.4.x (Didn't get access to any device with a version below that, hence couldn't test [Would be happy if you could let me know!]) Enough Talking, I've attached the Zip.
- Just Flash!
Enjoy! Don't forget to leave a Thanks!