The eventual winner in the space may well be whoever solves this: automatically figuring out which friends are more important to the user, making that measure invisible to users, adjusting it appropriately over time and then filtering to show everything from the most important as well as important updates from less important people while still allowing the user to see less important stuff from the less important people. The eventual winner could also be FB just on sheer forward momentum, size and how deep their hooks are into everyone.
I wonder if increasing bandwidth has also played a role in FB's declining engagement. FB was built as a pics and text based site but long term the trends will move away from this. Yeah it does video and music and everything else but they are stapled on. Over the past year I've watched my wife use FB less and less each night and things like skype and netflix more and more.