I've argued for a long time that Facebook has the huge advantage of having even reach most of the laggards. All other social networks that don't focus on an entirely different niche (like Instagram) will probably fail or stay small.

However, a social network doesn't necessarily need 800Mio users to be relevant. Even a small social network with an avid and interested user base can succeed.

And this could be the main differentiator here: A user base consisting out of people that love fantastic design. If they and their design-loving friends are on there, and don't require the facebook-laggard-surplus, then Path can succeed.