Crack the DRM and do it in a country that does not care about DMCA and has lax copyright laws. You could create an "illegal browser", and judging by how effective all the other antipiracy efforts have been to date (i.e. not at all), I doubt you'll face too much opposition...
Or go the "insert DeCSS here" route that some used back when that was a thing. "If you happen to have somehow acquired a WideVine lib, having hash [some string], stick it here if you want to watch Netflix."
Google can and does use DRM to block even this from happening: https://blog.samuelmaddock.com/posts/google-widevine-blocked...
Even Mozilla needed to license Widevine from Google to support modern video: https://support.mozilla.org/en-US/kb/enable-drm
Based on the policy evidenced in Maddock's post, it seems impossible to develop an open-source browser in 2019 that supports video streaming.