I’m unaware of any such project that operates on even a hundredth of the scale of the centralized sites that people want to replace. Facebook, Twitter, google, etc.
However, even a thousandth of their scale is enough to demonstrate that decentralized scale is possible at the level where there can be economies (or diseconomies).
Google's scale was already huge even when they had merely "more than 10,000 servers" in the years prior to their IPO.