Today, due to the volatility of the cryptocurrency price, I cannot say whether btc or altcoins will replace cash. This is the most important obstacle.
The point of the discussion is on the usefulness of Altcoins in the future,cryptocurrencies aren't replacing cash/fiat,take your mind off it..
@OP, even at this moment, most Altcoins are not that much significant,not to talk of the future,i think as time goes on the strength of the Altcoins would reduce tremendously,although we'll see a handful of worthwhile ones..
It's all down to how well the project organizes it's platform and the quality of its management team,Good Altcoins would survive,while the bad ones would gradually fade away