Yeah that is a cool feature for sure. With Advertising I'm not entirely sure that a totally decentralized mechanism for doing it wouldn't get out of control . You addressed the NSFW stuff but I fear that ICO scams and ponzi schemers could go out of control. Kind of like on CoinMarketCap there was Bitconnect and LaserOnline ads all over the place.
I don't know what the right answer is on that stuff because I'm sure a lot of people got sucked into that stuff through the ads but how much did it really hurt the reputation of CoinMarketCap by allowing those? Ultimately I still go to CoinMarketCap so I can't say it destroyed their rep and they made a lot of money as a byproduct of those systems