How can the decentralized cryptocurrency be controlled? The demand for it will be always an unknown thing. That is why Bitcoin cannot be ever stable. Its stability is in its growth, however.
There is a way if you ask me but the answer is so close to impossible it will not happen. I think there are two ways in order to make Bitcoin stable, the first one is making the investors connected to each other and talk to how much they will be selling and be holding to balance the price, which as I've said is impossible. Another is making Bitcoin a centralized crypto currency which is another that will not happen.