Well, alpine is weird, gentoo is big and openwrt is weirder.
So for now I am building void linux. The image is 2 gigabytes. Very basic image, spawns a getty on ttyS0
Username is root and password is voidlinux. The wifi stuff is in /etc/wpa_supplicant/wpa_supplicant.conf, add as many "network"s as you want, and that is my real wifi password. If you come to my house you can use it. Also nuke the ssh host keys if you want to use ssh.
For now the kernel is stock and only 1 i2c bus works, spi is non existent and ttyS0 works. Hopefully this will get better.
Chrony is included and configured so you can set the time right before using xbps-install as that uses ssl.
This is based on the cubieboard2 rootfs