If rolled out widely, this would make web browsers and third-party YouTube clients without a DRM license unusable for YouTube playback, download, etc. This would include almost all open-source web browsers and almost all third-party YouTube clients. Archive link to reddit post about this
It won’t kill adblockers, because adblockers don’t circumvent DRM.
DRM in the video feed would allow encrypted ads in the videos, and effectively break normal ad blockers.