Additionally, even though the copyright is expiring, the trademark is not.
“You can use the Mickey Mouse character as it was originally created to create your own Mickey Mouse stories or stories with this character,” Daniel Mayeda, associate director of the Documentary Film Legal Clinic at UCLA School of Law, told The Guardian. “But if you do so in a way that people will think of Disney — which is kind of likely because they have been investing in this character for so long — then in theory, Disney could say you violated my trademark.”
They don't give a shit about any R34 artist. They'll give a lot of shit if you start to make money, or diminish their brand in any measurable way - aka become popular enough to affect public opinion.