Youtube is hoping their premium model becomes as ubiquitous as Amazon Prime. At which point, ads will start appearing in their service. Because there is a captive market. A similar thing happened to cable TV and even Netflix is heading that way. You'll also never escape in-content advertising. Subway and KFC ads appearing in Korean dramas, etc. Content providers are going to maximize their revenue as long as they don't shed subscribers. Once enough people are paying for premium, the danger of inserting ads will vanish. Because everyone has premium and everyone else is inserting ads.