This tag has no purpose or ability to be used. If you search arttags:0 this will return posts needing an artist. Despite it being outlined in artist request that posts with links to profiles shouldn't have the tag, posts from Twitter, Pixiv, etc abound under it. Official art doesn't need to have the artist request tag either but frequently its tag is included on those posts and one can just search arttags:0 -official_art if they're actually gardening posts without artists.
The only reason to request an artist tag is in the case of a collaborative works where at least one of the artists is not known. This is a special case given that we must already know a post is a collaboration and very likely know at least one of the artists. Instead of a stab at the dark, there's a very reasonable expectation that someone in the community with more contextual or linguistic knowledge can determine the artists. We already have collaboration request which can stand alone so not this a reason to keep the artist request tag. The only space for improvement here I can identify is to separate collaboration requests dependent on being able to read a particular language from those that just require more familiarity with the artists and social circles involved in a post, which may include contacting the artists involved to see who else may have participated.
My suggestion is to remove artist_request entirely and instead have a permanent notice on the side of posts without an artist tag or official_art pointing out that one is missing. It should include links to the wiki that will assist people—in the case of posts sourced from Twitter, Pixiv etc. where an artist profile is available—in either creating or updating an artist entry.