A private blog for sharing photos is great, but the suggestion it's a Facebook replacement is questionable. People now use Facebook not only for photo sharing/status updates, but buying/selling stuff, communities, and (unfortunately) news. Notifications such as "Friend A commented on Friend B's post" is pretty impossible in this framework, and it's not really possible to recreate this in a world where everyone self-hosts. Projects like diaspora try a decentralized approach as the next best thing.
I would take this to mean a replacement for the "original" Facebook feature set, of sharing personal news, stories and photos with a pre-selected list of friends and family.
Many people (myself included) don't _want_ the newer marketplace / open community aspects of Facebook to be mixed into a platform where they share personal updates. If that means I have to give up 100 likes and comments on every baby/puppy picture I post, that seems like an acceptable trade-off to me. If folks want to comment on any of my updates, they can communicate with me in other channels (e-mail, text, real-life). Not for everyone, but it's definitely a market niche that's under-served right now.
I don't see anything questionable about this. Product A can be a valid replacement for Product B for only a subset of users.
A bike is a perfectly valid replacement for a car for the set of people who only drive a couple of miles to commute to work. It's obviously not a replacement for all users, but that doesn't undermine the valid claim that it is for some.
