As promised, here's a Proof of Concept Android build. It's very rough around the edges, but should give anyone wanting to build their own version of Android a start.
You need to first install the kernel for composite TV out
There is a bug in the current video driver that crops up when switching into Android mode, and it's fixed in that kernel. If you don't install the new kernel, you'll just get a black screen.
The image contains a "debugchumby" that creates a swapfile, reloads the touchscreen driver with precalibrated coordinates, mounts android.img as a loopback, and then does a chroot into it. The "android.img" is basically the contents of "out/target/product/generic/system" from when you actually build it yourself. The only patch I applied is that it supports ALSA, which at the time Android didn't natively support. This may have changed. These are all publicly available already.
It also seems very slow for some reason. I'm not sure why. And wifi support is kind of wonky. And so is audio. As is external device support. I'm not to familiar with how Android is set up, so these all may be very easy to fix.
If anyone can improve performance, I'd really like to see it. But in the meantime, you can take a look for yourself. Unzip to a USB drive and reboot. Note that because it creates a large swapfile on /mnt/storage/ the first boot can take a loooong time, and you can probably improve overall performance by moving everything onto /mnt/storage: