"Legally", could Elsevier get into trouble for offering unequivocal evidence that they don't care about their claimed copyrights and they don't actually consider Sci-hub infringing?
I see what you're saying about the journal contributing to the legitimacy of what they are purporting to be illegitimate, it's an interesting point.
I would like to add separately however for people unfamiliar with sci-hub, I am unaware of any copyright infringement issues of linking to or downloading from sci-hub. Sharing or downloading links has never been copyright infringement. Distribution is, which is why sci-hub is based in a separate jurisdiction (Russia I believe) that does not recognize US copyright claims.