Yes, this is possible using custom component but implementation could be little tricky.
1. Create a private board which accessible to superusers only.
2. Using jQuery add custom report link to the message options or you can add the button as well on the ForumMessage quilt.
3. On click on custom report link, you will need to create the same message on private board.
You can not send an email to the moderator using freemarker. However, superusers need to subscribe the private, so they can get the notification when the new message being added this board.
This is just a basic example how you can achieve this using custom component. You can enhance this feature as your need.
e.g
Currently, if we click on report content, it takes you to another page, where you can Notify Moderator of Inappropriate Content. You also can create a custom page and achieve the same functionality by provide user a Textarea.
I hope this will help you to start with this feature.
