To answer the Topic, no bitcoin will never replace fiat and anyone suggesting such doesn't understand the role fiat plays and why certain individuals will always use it to leverage control others. Bitcoin will continue to grow as an option for individuals to opt out of coercion and violence intrinsic in the nature of Fiat where they can transfer value voluntarily.
But the question is, can bitcoin really substitute dollar or other currency sometime soon?
Not until the confirmation issue is resolved. I wouldn't want to buy a chocolate bar and have to wait 10-30 minutes until my payment was confirmed. I want to pay and go instantly.
Odd statement.. All my bitcoin in person payments are instantly confirmed with payment processors. I suppose you want to get instant confirmations from girl scouts selling chocolate bars without a business ? In that case the lightning network will facilitate this : https://bitcointalk.org/index.php?topic=970822.0
Yes, once bitcoin payments become reversible.
This is trivial to do and is already being done with mutisig escrow. In the future we will start to see even more automated forms of reversibility with ricardian contracts (I.E.. open bazaar) What we do not want to do is remove the hard coded non -reversibility of transactions at the blockchain level as that is one of bitcoins main advantages that cannot be replicated by fiat ledgers in private databases between banks.