I've heard this a lot. I think there are two problems with this. First, you need massive adoption for the "social" part to be at all useful, hence only the few big social platforms can even try it. Second, even at maximum possible adoption, you'll probably run into the problem that actual human social networks have nowhere near enough branching breadth to help rank the behemoth that the web is today, i.e. for most queries and most possible hits, there's not enough signal coming from the social network.