There are two things a currency needs - wide acceptance and store of value. Your point about agreement can solve acceptance, maybe, if there is enough impetus to switch (like a failing dollar).
However as it store of value it fails because people holding currency do not want volatility. Dollars are created in response to increase in goods; bitcoins are created by algorithmic mining. There is a disconnect in creation vs. supply of real goods, therefore the value of bitcoin will fluctuate more. You might say that bitcoin's positive value increase bias makes people desire it over dollars, but that would cause people to hoard bitcoins only to dump and crash the market.
Now, you can adjust bitcoin by CPI, but then you'd just transform bitcoin into a system just like other currencies, along with entrusting a central banker and other problems.
The transactional advantage seems nice, but there is no reason a system can't be set up for dollars either.
I'm not going to say it's never going to happen, but it seems unneeded at this point.
However as it store of value it fails because people holding currency do not want volatility. Dollars are created in response to increase in goods; bitcoins are created by algorithmic mining. There is a disconnect in creation vs. supply of real goods, therefore the value of bitcoin will fluctuate more. You might say that bitcoin's positive value increase bias makes people desire it over dollars, but that would cause people to hoard bitcoins only to dump and crash the market.
Now, you can adjust bitcoin by CPI, but then you'd just transform bitcoin into a system just like other currencies, along with entrusting a central banker and other problems.
The transactional advantage seems nice, but there is no reason a system can't be set up for dollars either.
I'm not going to say it's never going to happen, but it seems unneeded at this point.