This leaves just -o and -e from the nextboot shell script, which isn't as careful as reboot, to be implemented.
I plan on replacing the nextboot.sh script with a symlink and different behavior (not actually rebooting).
It's the lessor of the evils of having our nextboot protocol in multiple places, and continuing support for it in reboot.
The extra code is small (< 2k) and having it all together eventually is good.
Though Kyle did mention a libnextboot, I didn't take that next step because nothing else knows about this protocol from this side of the fence (of course the loader knows...).