Yep, eventually ads will creep their way into the payed system.

At the end of the day, there's no such thing as enough money for corporations.

Even when you aren't seeing ads their algorithm is still controlling your front page, allowing them to push partner content that isn't directly advertising but still acts like it. The differences between a commercial for Doritos and an episode of Good Mythical Morning titled "Trying Every Doritos Flavor" from the perspective of the PepsiCo marketing department are that people might willingly click on the GMM video and they probably didn't even have to pay anyone for the video to happen.
Sure Rhett & Link may not have a partnership with Pepsi and are just innocently making content to give their audience (I genuinely believe this), so they've got no part in this becoming advertising, but you would have to be incredibly naïve to believe that Google's algorithm isn't smart enough to recognize that video and others like it as marketable content the promotion of which can be sold to PepsiCo.

Premium subscribers may not be seeing ads, but they are absolutely still seeing advertising.

edit: typos