The vast majority of their userbase already puts up with it, so I doubt they will see any significant backlash. Even if all the FLOSS creators leave, they're still a tiny minority because it's """influencer""" channels like the Pauls and content farms like Bright Side that are the real cash cows on the platform.

Also, a huge part of their userbase is children. Probably more than any other mainstream social media platform. They won't even understand the concept of DRM or corporate bullshittery and will only use the YouTube app or browser anyway. Kids are also less likely to be bothered by ads, might not even understand what the purpose of an ad is, in fact they will just see them as more content which is why advertising to kids is so unreasonably effective.