I would like to have an fedora or centos image available in LuCI
Well, in LXC templates: Fedora and Centos support?
it was stated: “unfortunately there is nothing, what we can do right now.
AFAIK Fedora and also CentOS doesn’t provide armv7l tarball rootfs.”
In Creating lxc containers for distro not in template list
you can learn how to make one yourself.