I made a paid request on a mod like this a while ago.
What the mod i have on my forum basically does is that lets me choose by forum id the sections that I want the posts to be posted as anonymous. I created a user in my forum named anonymous_reporting and in whichever section the mod is enabled certain usergroups will see all threads and posts posted by the user anonymous_reporting and others will be able to see the real names of the users who made the thread (depending on the mod settings)
This is how a user will see the posts: (all usernames replaced by "anonymous_reporting")
How the admin/configured usergroups will see the posts: (can see all the real names)
Settings:
I can choose which usergroups' posts will be posted as anonymous_reporting and to which usergroups it will not take effect (my forum staff)
if you want this i can share with you, let me know.