My advice and wait for a flashable image. This isn't going anywhere and it will only improve with time
I'd rather get a Mibox.
All of those steps and you may brick your device? no thanks.
I have a Fire Stick laying around that I had acquired to test out Playstation Vue (before they came out with the Android TV version). I might try and get this working on there. Awesome stuff.
This looks really cool. I don't even have an AFTV device, but I kinda wish I did, just so I could turn it into another Android TV device.
Update: I took the plunge and tried this on my fire TV 1. Everything is fine and I'm now running a leanback launcher with the play store on my fire TV. Finally my legally purchased DroidMote works without play services meddling. Voice search doesn't work (but text does) along with a few options for obvious dependencies that are broken still. Going to load SPMC on it and see if it populates recommendations.
BTW... Update on the pre-made image. It's probably not going to happen due to legality the OP said. This project has many files that need the original authorization from each developer to be distributed. This method is probably going to be the only way.
On a side note: does anyone know how to install the Prime Video app on the NVIDIA Shield?
On a related note there are a number of unofficial Android TV ROM's floating around, this would be the pick of the lot of them due to integrated, inbuilt TV Tuner / PVR support: http://wetekforums.com/v/index.php?p=/discussion/30398/rom-play-2-marshmallow-android-tv-v2-2/p1
Install is no harder than easy Rebooting to Android Recovery and Flashing new .zip Firmware.
After reading what needs to be done I'd rather buy a Nvidia Shield haha