I actually use Fedora IOT in my datacenter rack to access my switches over LTE in an oh shit scenario. My uptime on my RPi3 B+ has been fantastic with this flavor of Fedora. I plan on switching over to FCOS on a RPi 4 soon tho.
I'm currently running Fedora IoT on a pi4B, it works very well for its purpose (running containerized services on Podman+Nomad). What does CoreOS offer over IoT?