Cryptocurrency replacing fiat will certainly never happen. Governments and central banks will not allow that to happen. Cryptocurrencies will be the trend in the future and will exist alongside fiat. Cryptocurrencies give people more options in their payment methods or become another trusted place to invest and store assets.
Now we think replacing fiat with cash is impossible, but with the progress of the project continuing to improve I have no doubt that it could happen soon. Before that happens then we better focus on investing bitcoin.