I do not think Bitcoin replaces Fiat today for these reasons:

1. Not trusted. Simply put Bitcoin has value in the market place just not with any of the vendors or people i want to do business with. My local online classifieds returns 9 ads that mention Bitcoin, out of about 100,000 new ads a month. 9. Two years ago it was 15 hits, so trending to zero???
2. Not portable. Setting up my phone wallet is scary as hell and most certainly not close to mainstream yet.
3. Not fast. I cannot complete a person to person transaction in less than 20 minutes.
4. Not scalable. If I solved 1-3 above, the network would fall on its face.
5. Not anonymous. Not a huge deal but nobody is tracking what I buy at garage sales today if I use the good 'ol dollar. Imagine me buying crap from a guy that turns out to be thief and a drug dealer. Nice eternal paper trail i have left behind.

I am long Bitcoin, but right now very long. I put this list together thinking about how far we are from true mass adoption. My answer.... we are a long, long way out. It really is all about the marriage of software and hardware.... Very complicated problems that will take years and years to iron out. Every mistake leading to losses of millions in stolen coins. This ecosystem is a brutal teacher, if your solution isn't perfect you will lose everything and so will everyone that trusts you.

I think it will take 10-20 years of software improvements to solve our current problems, and in the mean time.... I think the price will go lower. Maybe even for years.