I don't agree with creating separate pages solely for illustrator fanart. For most galleries it would be equivalent to making a page for one piece of art, and it still has that problem of linking the artwork with the character to the article full of canon information. I still think that we should instead put that art in their respective illustrator pages, to clarify that it is solely appreciated for its artistic value in relation to that artist, not because it has some importance or relevance to the character articles. Because it doesn't (unless the art in question is specifically presented as concept art, which if it was, it would already be in the concept art tab).
And I really don't think we should be referring to any of that as "illustrations" because as has already been said, it implies that it's somehow a canon depiction of what it's showing. It doesn't matter if the fanart is made by official artists or not--fanart is fanart. Ichika might stick to her designs pretty strictly but there are gaps in her knowledge just like anyone else, and that's not even getting into the liberties taken by other illustrators in their non-official work.
I agree with categorizing images, though I'm not entirely familiar with the logistics of all of it.