If you carefully read that wiki definition you quoted, you'll see that there is a slight problem with this set of implications:
When a character shows a fang or fangs outside a closed mouth.
Fang_out, per its definition, may be used when both fangs are visible. As things stand, fang_out can't implicate fang because fang is only for a single visible fang. That's why this very same implication was rejected several years ago.
As for fangs_out, it was created comparatively recently, presumably by someone who didn't know that fang_out could be plural. It sees little use, because most of us know to use fang_out + fang/fangs, and also due to neglect on the part of its users. It has no wiki, and other wiki pages don't link to it. I wasn't even aware this tag existed.
If there's a movement to redefine fang_out to only be singular, and make fangs_out "official", I'd be okay with that, but keep in mind that there will be some manual cleanup involved for images like post #2349393 and post #2845900. Alternatively, we could just alias fangs_out to fang_out and continue tagging fang or fangs as necessary.
As for implicating closed_mouth, forum #121965 summarizes my feelings pretty well.