Hello @david,
A workaround is simply to give a hostname to your IP address, by editing /etc/hosts or its equivalent on your OS.
192.168.0.1 localhost my.localdomain
And you can now register my.localdomain as a CH API “JavaScript domains”.
Still, a status update would be appreciated, for something that was already on the backlog in 2015.
Just remove the piece of code preventing localhost as a valid domain name, and you’re done.