I think we should add this.

However, gnome-initial-setup is a bit late because currently anaconda
uses hostname to name your btrfs subvolumes. :(

anaconda would perhaps be a better place, but only if it uses hostnamed
so as to allow spaces, Unicode, etc. We don't want anaconda to use
stricter rules for hostnames than the installed system does.

I think we currently hardcode all live images to have "localhost-live" hostname in the kickstart, because of some x11 bug a long time ago which failed with a plain "localhost":

Changing it to "fedora-NNNN" would be great.