Root fs backup on reboot / dual boot SD card

I remove my SD cards from my HC2s and clone them offline. Works fine.
But I figure that it should be possible to configure OMV to use two root filesystems while booting.

On the card there might be three partitions:

boot - this is the normal boot partition.
rootfs - this is the normal root fs with OMV.
rootfs2 - this is a new minimal root fs.

OMV first boot to rootfs2.
A script in rootfs2 creates a new offline snapshot off rootfs. Stored in rootfs2? Or somewhere else?
A script in rootfs2 reboots to OMV in rootfs.

Then in rootfs the updated snapshot may be copied to some other location, possibly on the network. Also old snapshots may be deleted so that perhaps only the latest five are kept. After/before updating or changing the configuration all that would be needed to perform a system backup is to reboot. It might even be possible to add an option to revert rootfs to the previous snapshot, and reboot. A little like timeshift.

Could this work? Can something like this be implemented in OMV, perhaps as an option if the boot media is big enough? With 32 GB SD cards or thumbdrives it should be fine.

Or perhaps as a DIY hack of the boot process? Can you reboot from one root fs to another rootfs? Or do you have to update the boot partition and then reboot?

Is this something that someone already is doing? If so, please comment.

Storing the snapshot on the rootfs using a COW snapshot sounds nice. The only problem being that I so far have managed to stay very ignorant about the details of using the btrfs COW snapshot features. I just know they exist. Oh, well... I'll just have to google and find a btrfs 101 snapshot tutorial.

The snapshots will still have to be copied elsewhere to keep safe from card failures. But as long as the card is OK the btrfs snapshots should be available for a total revert to previous config.

Also I think I can figure out how to change what rootfs to boot to.

The remaining problem is that it would be nice if it was possible to reboot directly from rootfs1 to rootfs without having to change anything in the boot partition. Otherwise the boot partition has to be updated twice during every boot sequence. Once to reboot from rootfs2 to rootfs and once to boot to rootfs2 after shutdown.

For rootfs I might use Armbian? Perhaps a cut down version? Or is there a really small minimal ARM distro that could be used only to run a few commands to create the btrfs snapshot on rootfs and then reboot, possibly after modifying the boot partition?

And as @gderf says, if I want to write a fresh SD card, I'll need a copy of the MBR and the partition table as well.