Also have a look at https://en.opensuse.org/Kubic:MicroOS

It uses btrfs instead of OSTree. It only allows writes inside /home, /var, /tmp, /etc, ... and everything else is updated transactionally.

As a user of standard Fedora, what would this give me?

Configuration of my system is mostly easy when setting up (dnf install xyz, plus 2 config file tweaks in /etc). It's the config of everything in /home that's complex (gnome settings, my emacs, bash and git config etc.).

Its immutable, so painless upgrades without worrying about a borked package that systems tend to have after you've been running across major releases. It also grabs most desktop apps through Flatpak, so in theory more frequent releases of desktop software.

It's a trade-off. I like it because I want a system that always works and updates silently, and I don't make heavy customizations. It's probably not for you.

It also has support for podman, which runs using user namespaces. Still a bit rough around the edges (fuse-overlayfs still a bit buggy and not POSIX, the same way that overlayfs in the kernel was initially buggy and had to wait until overlay2 to have it work reliably with docker)

Not actually heard of that - will take a look thanks