According to https://docs.github.com/en/site-policy/content-removal-polic..., even an upstream dmca doesn’t suspend downstream by default (unless the copyright owner claims they believe all forks violate copyright) — so I would be surprised if downstream dmca suspended upstream.

NB: according to https://www.gtlaw.com/-/media/files/webinars/ian-ballon-may-..., page 4-470, it’s possible that failing to process a DMCA notice may only lead to losing safe harbor for the material identified in the notice, not for the entire service.

So GitHub might just choose to ignore the notice for React, get sued, and win, all without losing the safe harbor.

For less popular repos, I would not be surprised if you could take down any repo literally by submitting a completely bogus notice.

But honestly I still don’t know how much leeway - legally - service providers have in applying their own technical/legal expertise when evaluating DMCA notices. I’d appreciate any sources (court decisions, textbooks, whitepapers, descriptions of actual industry practices, etc) on the topic.