That sounds very, very hard to implement on an aging SMF codebase that can barely crank in patches without introducing other weird bugs.

Isn't it possible to hide user information on threads if they willingly want to make a post anonymously?
We should have a checkbox on the post-writing screen, somewhere around the "Post" and "Preview" buttons, maybe above them and below the textbox where we write our posts. The checkbox should look like this: Post anonymously: [checkbox]
Those who mark the checkbox and then press "Post", their post should get posted, but all their information should be hidden. The space where user information is shown should only say "Anonymous Poster" with no href, which means the username shouldn't be clickable. There should be no profile or anything behind it.
This will allow anyone willing to make posts anonymously so they are not judged or attacked personally. No posts, merits, trust, avatar, or signature will be shown, which could make someone understand who the poster is or their rank in the forum.