My take from the article is that Bitcoin, as cryptocurrency, is a mechanism that can be used to replace fiat money. It will never be because of exactly the reason the article says: there will be a maximum of 21 millions Bitcoin and that's all. And since the current mechanism behind fiat money is inflation (usually you want to have a slow inflation, not a fast Venezuelan one) is what drives people to spend them and create economy - this will never be applied to Bitcoin ever. Hence you get deflation in case of Bitcoin, which drives people to amass them instead of spending and you get in the end the current purpose of Bitcoin -> art like investment.

The only way to make them a currency is, keeping them limited to 21M, is to create some sort of "bleeding" mechanism where you force the owners to spend them (spend or lose) - which will never be implemented.