The article does implicitly address why this is an alternative to Facebook. "We feel that your work life and your social life have been well-addressed online, but no service has truly helped you stay in touch with your family".
Facebook is not for intimate conversation with your family. Path is mobile-first and isn't as big of a thing (yet). Google+ allows you define circles but is rather complicated. As with other spaces where network effects are important, only the biggest will survive and the biggest currently (Path/Google+/others) do not address the family niche conclusively (product wise/platorm wise).
The real question is whether the family niche itself is an important enough one to a large enough base of people. It makes more sense to assume that this is the case...than not right? The upside here is pretty huge if there's something to it.
Facebook is not for intimate conversation with your family. Path is mobile-first and isn't as big of a thing (yet). Google+ allows you define circles but is rather complicated. As with other spaces where network effects are important, only the biggest will survive and the biggest currently (Path/Google+/others) do not address the family niche conclusively (product wise/platorm wise).
The real question is whether the family niche itself is an important enough one to a large enough base of people. It makes more sense to assume that this is the case...than not right? The upside here is pretty huge if there's something to it.