Feedly doesn't really sort by Popularity. Instead they simply load ca. 20 entries and select the three most popular entries on the client side as Featured. That being said at scale you have to compromise one way or other.

The Idea behind my popularity algorithm is that I don't want to calculate what is popular among the Users of my service. Instead I want to estimate what is popular with the original User base of each Feed you subscribe to. I think the average User base of The New York Times is different from the typical reddit, twitter or facebook crowd. So this should be an interesting Differentiator.

I'm significantly more excited about your beta now that you've explained it. I think that's a unique and a potentially great way to do popularity ranking.

Fingers crossed that you're also going to have an eye for security