Such a feature would pose many security issues, which is one of the reasons we haven't added it. We'd have to give the web interface access to change the root-owned /etc/hosts file, which might be overcome by adding the hosts instead via dnsmasq's config files. Even then we can't prevent a user from misconfiguring their system on accident, which would happen more often if there was an easy GUI than if they had to more fully understand what they were doing when manually making the changes. We may still add this feature in the future, but for now we have decided to work on other things.