More for reference than really arguing that anyone should use it, here is an attempt I
made at scripting essentially what Chris recommended.
https://github.com/gregory-lee-bartholomew/bootsync
I actually do use it on a few of my Fedora Linux systems. Unfortunately, it relies on
systemd-boot instead of grub. So it is probably a no-go for being included in Fedora
Linux, at least for now. Also, there is a race condition in the current version where it
sometimes fails because the A/B partitions aren't mounted yet when it tries to
"rsync" the contents between them. I think fixing that is just a matter of
adding something to one of the Before= or After= settings on the systemd unit. But I
haven't traced down that problem just yet.