What I found out, is that you can spin up a Host on the Hetzner cloud service with ubuntu. But when the Host is running you can go to “IMAGES” and choose CoreOS there (also rancherOS or Alpine, and some others). After a restart of the host, it should run on the choosen (CoreOS) one. I wrote them that they should include that in host creation process. Maybe some of you will write them too. Should not that problem to implement that in their infrastructure.
This would be awesome.