Well, for one, you are welcome to copy the entire contents and start your own wiki. A good portion of the infrustructure is ready for you to use too. Wikipedia is, in effect, a node which you can fork anytime. If the central authority (Wikimedia Foundation) fails the content can still exist.

Then there's the blatantly obvious way that defines the uniqueness of Wikipedia. Decentralized content creation and editing. Yes, there is still a central authority that regulates it, but you can fork and make your own editing rules if you wish.

These are obvious to most. They are not ideally implemented, optimized, or well distributed decentralization, but that technology, ready to take on the scope of wikipedia, is waiting to be invented. It's still a huge step away from the centralization of Encyclopedia Britannica.