There isn't a single lasting mass consumer adoption example of decentralized anything in the modern history of technology (eg post WW2). That's due to a rigid reason: human nature. It's not going to change.
The only thing that will change here, is privacy laws will force behavior changes on centralized platforms.
I can name dozens of massive technology & platform adoptions by consumers, every single one of them is centralized. Now, name the dozens of vast decentralized examples... crickets.
Decentralized as a mass consumer adoption thing will perpetually be fantasy. Only (some) tech people want it.
By the way, the sun is decentralized, its center of gravity does not coincide with the galaxy's center of gravity!
Good comment anyway. I didn't even think of e-mail.
But don't hold on to those shares for too long.
The mesh/decentralized/p2p networking movement is really interesting, and given the ever increasing power of user devices, the balance for a shift to those models is compelling.
There are huge existing challenges, but I'm seeing really smart ideas in the space, and I think it's only a matter of years before we start to see mainstream p2p networks (still over the Internet) replacing a server model for some successful widespread apps or services. Facebook style social networking is the PERFECT use case for such a topology.
Facebook's time is coming to an end. Not now (like some are reacting), and not in the next year or so, but soon enough. Their paradigm isn't as good as the alternative. The alternative simply has implementation issues that need to be worked out, but they aren't insurmountable, and different groups of people are solving them in novel ways constantly.