Now when you go to their site, it reads:
Repository unavailable due to DMCA takedown.
This repository is currently disabled due to a DMCA takedown notice. We have disabled public access to the repository. The notice has been publicly posted.
If you are the repository owner, and you believe that your repository was disabled as a result of mistake or misidentification, you have the right to file a counter notice and have the repository reinstated. Our help articles provide more details on our DMCA takedown policy and how to file a counter notice. If you have any questions about the process or the risks in filing a counter notice, we suggest that you consult with a lawyer.
Also at 9to5Google
[2020-10-25 01:01:09 UTC: Updated title to more accurately reflect notice was given to GitHub, not to youtube-dl. --martyb]
(Score: 2) by loonycyborg on Saturday October 24 2020, @09:45AM
It will not affect its legitimacy in the slightest since all people who use it already know that copyright law as understood by RIAA and their workflows are in irreconcilable clash already. And I don't think that this takedown will actually legally hold in case if a counter-notice will be sent.