There's that, but aren't lewd Ellen Baker pictures frowned upon by Pixiv now?
Not really. This topic is surprisingly poorly covered, but from what I've read: there are no restrictions on submitting R-18 art with her. What is restricted is tagging, both artists and users are asked/required to not tag lewd Ellen Baker art with "New Horizon" or any of its variations. Pixiv is doing this to dissociate such art from the book.
Personally, I don't see much point in it, but whatever. It's no big deal as long as they won't go any further.