But bitcoin doesn't work that way. Bitcoin works like every other commodity in this planet. It's about demand & supply. As the demand grows, the price will grow in accordance. The dev of bitcoin put an underlining mechanism called network difficulty. This mechanism will ensure the scarcity of bitcoin, protect it from oversupply and frequent price bubble burst. And bitcoin now isn't just a commodity - it's a currency. As economy grows, the demand for money also grows. So it's not just about how many people left to adopt bitcoin - but as there are more and more ecom platform, or even brick & mortar business, which accept bitcoin as payment, the demand will only grow.