I don't think it's a good idea. While there are some aspects that warrant actual discussion, I presume a thread on this would easily turn into endless crank-yanking over what people should or should not like/dislike, unaware incompetents refusing to take valid feedback, conspiracy fuel, and pity partying about how unpopular one's preferred subjects/characters/kinks are compared to hetero smut featuring big titties.
If all downvotes are legit (i.e. not due to filterable content), there's little to be done besides improve the art.
If it's actually downvote-bombed, the reason may be
- poor tagging causing it to leak past the filters of people who would have never seen it had it been comprehensively tagged
- someone hate-shared the image
- someone is sockpuppeting
- and the classic, people-not-filtering-things-they-should-be-filtering.
Out of these, only tagging is something the artist/uploader can do anything about on their own.
And I do think we already have topics that cover "what can I improve about my art?" and "any tags I should add?"
/edit: And yes, as mentioned above, this sort of topic would definitely attract the types who are looking for validation instead of honest feedback, and will get very pissy if offered real feedback instead of a hugbox.