>>105608909
I'm now this far:

>build /, /boot and /initramfs
>initramfs just copy of root for now
>/init script for initramfs that mounts stuff and gives shell
>/boot and / on separate partitions
>everything scripted to build into single image file that you can boot

But I don't know how to switch to the root partition from initramfs, not yet. If I exec busybox's switch root it gives me kernel panic.