The problem with the DMCA takedown process is that it makes it easy to get information removed without having to prove anything, so it does get used for censorship (and harassment of competitors and to force anonymous speakers to choose between being silenced or revealing their identities in a counter-notice and ...)
It's pretty much the go-to thing for anybody nefarious who wants to have something censored without all the trouble and blatant impossibility of having their claims vindicated in court.
This code is meant for censorship, not DMCA. Replacing the content with "sorry, this thing broke copyright laws" is how you deal with DMCA, not stopping people from accessing whole sites.
That's what I was thinking as well. DMCA is just an excuse. Github already blocked content at the request of Russian government, and I'm sure they will block more stuff that they're not legally required to remove in the future.
Er, citation required? IME they do what's required by U.S. law and have previously been fairly principled about not complying with extrajudicial requests.
This status-code is a great solution to inform the public about it.