I agree that it's completely unsolved. I work in mobile robots and it's just maddening the number of solutions which either won't work if you're headless or won't work if you'll need kernel upgrades, or won't work if you'll need seamless rollbacks, or won't work if you'll want OTA updates or won't work if you'll need to be able to reconfigure the network in-band (not by exiting your app for some outside management GUI).

We ended up with a mostly hand rolled system based on kexec, grub chainloading, and deploying rootfs images as big tarballs. It works, but I really wish there was something we could have just taken off the shelf.