After Google Reader launched, other companies built basically the same thing, and some of them flourished after Google Reader was shut down. But none of them have met all of the above points.
instead of investing and figuring out a way to get your existing user base to contribute content to your new social network, you kill that user base and say that they have to transition in ful to google+. Instead, people were like "we're all talking about things on facebook, I'll just share the articles there"
google+ should have been a data platform with many different front ends (reader being one of them, the facebook clone being another). Instead they just wanted to make a facebook clone.