Technically it is possible that 1 Bitcoin could eventually be worth 1 million dollars, I doubt it would be in our lifetime. If you think about how the US dollar can buy less every year because of inflation, this means the US dollar drops in value every year. At the same time that the dollar drops in value, Bitcoin theoretically will increase in value every year because there is a limit to how many there will be in existence and the mining is getting harder. Also, Bitcoins are constantly lost and can't be recovered. So over time, Bitcoin should continue to increase in value compared to the US dollar. If they are both around long enough, 1 Bitcoin should eventually be worth 1 million dollars.