Thanks Glenn for that question. Let me begin by discussing the role of government, and then turn to the private sector.
In short, government should impose no mandates on anyone. As you note, Republic.com argued that government might consider certain responses, intended to promote exposure to diverse positions. Fortunately, the discussion was tentative and didn't endorse any of those responses. Unfortunately, those responses would be unjustifiably intrusive, a bit silly, and even unconstitutional. For that reason, I'll omit the details, thank skeptical readers for their convincing objectons to what I suggested, and confirm what you say, which is that Republic.com 2.0 rejects government mandates (and says that they would be unconstitutional).
Any responses should be private. By way of introduction, let's recall a really impressive moment from the most recent election: Senator Rick Santorum's concession speech. Santorum began by praising Bob Casey, saying that he was a fine man and that he would do a fine job for Pennsylvania. Then he specifically asked his supporters to give a round of applause to Casey. Here's the best part: When the applause was tepid, Santorum added, firmly and spontaneously, "Come on, give it up, give him a round of applause!" There was real grace, and charity, in what Santorum did.
For the blogosphere, here are some small ideas. If you're a liberal blogger, you might include some good conservative blogs in your blogroll. If you're a conservative blogger, you might include some good liberal blogs in your blogroll. It might make sense for bloggers to develop an informal norm of reciprocity. If you have a clear ideological position, and find yourself linking only to people who already agree with you, it might be worthwhile to include a few links to people who don't agree with you -- emphasizing that they might be right on a particular question, or at least that their view is reasonable and worth considering.
Orin Kerr, at the Volokh Conspiracy, is a terrific blogger, in part because he seems to me a model on this count. His own views are hard to characterize, but he avoids contempt, and better still, he tries to make the best, rather than the worst, of opposing positions. He doesn't attack people's motivations; he assumes that people who disagree with him are acting in good faith (and that they are unlikely to be making obvious errors, and haven't lost their senses). And with all this, he can be quite funny.
Of course some positions are unreasonable; no one needs to link to those who argue that the attacks of 9/11 were an American conspiracy, or that slavery was, and is, very good. But our topic has been the division between Red States and Blue States, or conservatives and liberals, and it would be pretty amazing if it turned out that one or another side has a monopoly on reasonableness. (Actually it would be amazing if it turned out that political life is sensibly understood in terms of two "sides.") For readers, knowledge of group polarization, and its effects, should be able to provide a degree of inoculation.
We've been discussing some of the risks, but much of your work has emphasized the amazing potential of the blogosphere to aggregate dispersed information, in a way that is likely to produce a lot more knowledge than a world dominated by the mass media. (Cf. Hayek's critique of socialist planning as compared to the price system.) You're right to emphasize that potential, which is only beginning to be realized; it's a key point when considering the state of the blogosphere.