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.