It's all about track record. That's what the guy from Virgin Trains said on the radio this morning. No-one I can think of has a better track record than Ev Williams (Blogger, Twitter, Odeo), so Medium and Branch are of interest.
What is Medium?
"Medium is designed to allow people to choose the level of contribution they prefer. We know that most people, most of the time, will simply read and view content, which is fine. If they choose, they can click to indicate whether they think something is good, giving feedback to the creator and increasing the likelihood others will see it."
Voting - what stops it turning into Digg?
Branch: "Between articles, blog posts, and tweets, the internet is dominated by monologues. So we want to build a home for dialogues online, by combining the intimacy of a dinner table conversation with the power of the Internet."
It's not clear how filtering will work here - how do I limit the noise?
Ultimately, these sites can only succeed if they avoid becoming yet another destination - they don't have the leverage that Google has with Google+. I have a model for a social network that is bound to succeed - pay me or my contributions - on some sort of sliding scale of micropayments based on popularity. What I don't have is the business model to fit.