When the checkpoint rewind will be select we will show the BE version
before the checkpoint was made.
In general, it seems nice. I'd like to see more for description; how the checkpoints would appear, what it means to the boot process, would it mean updates for some manual/handbook? It would nice to refer to zpool, not all people do know where to look for information.
I can not tell much about lua bits, but the rest seems good. I was starting to think if using ! is complicating things (could just use environment variable - those are accessible via kenv), but I'm all good.