While playing with tiny configurations I removed the UCI package via menuconfig. I think this is what made the image fail to come up correctly, in that the kernel booted but various /etc/config files were empty so basic services like eth0 weren't available, and trying to fix them with init.d script execution via a serial console gave UCI errors.
Is UCI required by design and ought to not be removable, or should it be removable and the relevant scripts be made UCI independent? My own preference for keeping tiny device running would be that would direct editing of config should be enough, so UCI removable.