Hypothetically, should bitcoin become the only money used around the world, it will no longer have large room for growth in value. At that point, demand for it will simply be demand for holding liquid money, and the speculative investment aspect of the demand we see today would disappear. In such a situation, the value of bitcoin would vary along with the time preference of the entire world's population, with increasing demand for holding bitcoin as a store of value leading to only small appreciation of its value.