Using a $20 CPM [1] (Cost Per Mille, the money advertisers pay per 1000 views), $12 turns out to be 12/20 * 1000 / 30 = 20 ads per day. I would argue that the average youtube premium user watches less than that.
And I would argue that youtube really knows the numbers, and google would not lose money. Don't forget they've turned evil ;)
The main problem with this analysis is that not all Youtube viewers are of equal value to advertisers. Premium subscribers are the people who have demonstrated that they are willing and able to spend money on luxuries. These are also the primary audience of advertisers (compared with, say, the elderly living off welfare, minors without a credit card, people living in poor countries).
Every premium subscription Youtube accepts reduces the value of its ad-supported audience, not just in an absolute sense (i.e. this user won't watch ads anymore), but in the sense that it lowers the CPM advertisers are willing to pay for the remaining “cheapskates”. The premium subscription price has to account for that, which is why the price should be significantly higher than the average ad revenue per user.
Using a $20 CPM [1] (Cost Per Mille, the money advertisers pay per 1000 views), $12 turns out to be 12/20 * 1000 / 30 = 20 ads per day. I would argue that the average youtube premium user watches less than that.
And I would argue that youtube really knows the numbers, and google would not lose money. Don't forget they've turned evil ;)
[1] source is the most recent Big Time video