Guess, who is the bigger ad placement in the world?
Yep, it's Google and Youtube: they have a targeting by interests (themes of video) + targeting by geo/demography (video watchers) X scaling with an increase in the number of views from subscribers (video quality/hype/viral/etc).
This a great example of an "endless" growth loop of metrics and money.
So, why not use this model for Netflix?
Netflix could offer non-payment plans and next grab profits via showing video ads (like it used on Youtube or classic TV). Users, who want to stay with money payment plans are still free from ads.