Anything is possible, but their entire business is built around a centralized model. It's what enables them to support so many users and so much activity, which enables them to make a lot of money through ads. Decentralization requires giving up a lot of control, and increasing costs dramatically. It means becoming a totally different business, and most businesses have difficulty surviving even when they are just maintaining their existing model. Those businesses that do survive major technological shifts, like Apple, typically do so by totally transforming themselves, but most die in during that process.