I have an article titled "Viewpoint Diversity" Requirements as a New Fairness Doctrine forthcoming in the George Mason Law Review. A draft of the article is available here. The material below omits the footnotes; if you want to see the footnotes—or read the whole draft at once—you can read this PDF.
The article draws an analogy between the Fairness Doctrine and viewpoint diversity requirements.
One of the problems with the Fairness Doctrine is likely to also arise with viewpoint diversity requirements.
Author's summary: Exploring viewpoint diversity requirements.