spending their btc.
Here are ways in which increased adoption could increase the supply or reduce the demand:
1. Velocity -- increased adoption will make bitcoin transactions more liquid. Fees will drop and it will become much easier to obtain bitcoins and exchange them, and there will be less need to hold them. So, where it now takes 11 million BTC to power the economy, in the future it could take much less. Demand will drop as a result.
2. Fractional reserve banking -- At some point when Bitcoin has become more mainstream, a fractional reserve banking system may develop and the supply of bitcoins will double or triple, or more.
3. Reduced savings -- As the exchange rate begins to stabilize, the return on holding bitcoins will drop and people will be less inclined to hoard them. Spending hoarded bitcoins will increase the supply.