Ultimately, I think a system like youtube is the best revenue model. Separate the ad and the normal content, and make it so that the ads benefit the users as well as the producers. Producers get ad money, youtube gets ad money, and consumers get good content.

Users know their time watching ads goes to create what they love, and will enjoy and often disable adblock or chose to click ads to help the creators as well. Ads will appreciate this fact, and will be willing to use a system because their content becomes inherently, or more, positive in the long run, making a better impression.

Secondly, if you have a strong ecosystem, you can use ads to allow users to promote communities, or other systems, assuming it isn't their own. Imagine you could pay to promote a favorite subreddit, or pay to promote some comment, like with reddit gold, but intentionally in a way that moves comments into their own, special, well-seen group.

Abuse of that system would need heavy monitoring, but it would be a good way to get a lot of money.

The modern trend, with kickstarter and other systems, seems to be leaning towards the trend of user-funded, and user-profits. Hell, you might even say that websites are going to start becoming F2P.