Not sure about the Future of CoreOS, though: "With the acquisition, Container Linux will be reborn as Red Hat CoreOS, a new entry into the Red Hat ecosystem. Red Hat CoreOS will be based on Fedora and Red Hat Enterprise Linux sources and is expected to ultimately supersede Atomic Host as Red Hat’s immutable, container-centric operating system."

https://coreos.com/blog/coreos-tech-to-combine-with-red-hat-...

The Flatcar project wants to keep the original CoreOS alive, however: https://www.flatcar-linux.org

Recently started using CoreOS for Docker Swarm, and it seems really promising. I wonder how this compares?

Really good question. The short version is that CoreOS is a generic container based distro. Talos is not. It is designed with the goal of making a machine a Kubernetes node in a fast and reliable way. We don't use systemd, but a pure Golang init that is Kubernetes aware.