Downloaded all apks on my minix neo x7 running 4.2.2. Can confirm that Leanback launcher, Media shell and Launcher L cannot be installed on Jellybean.
Leanback Keyboard however, installed fine. I was able to set it as my default keyboard and move through the different characters with a dpad on a remote I have. Unfortunately I wasn't able to press any of them. The enter key on the remote I use didn't press any of the letters, but instead hit enter.
Soon this set top box is gonna receive a kit Kat update, so I'm crossing my fingers I can get any goodies from android TV working on it.