I guess a question would be: If you have the cash now, is it smarter to do it all at once or DCA over a period of time? Certainly if you don't have the fiat now, DCA is smart. If you do have it now and the alternative is to invest it over 4 years (roughly the time period in the article), I think the better advice is to just buy it all now or as there are dips and then don't trade it.
As for $1 million, if enough people are buying then it could easily happen. 1 to 3 more orders of magnitude is certainly possible until there is some sort of fiat equilibrium reached.
This actually made me think now that there are several kinds of DCA:
1. Buying a fixed fiat amount at regular intervals, which I suppose is the true DCA strategy of enforced savings, since it averages out the dollar buys.
2. Buying a variable fiat amount at fixed intervals -- e.g. Whatever is left aside every X weeks is put into buying BTC. This is my DCA, albeit, in reverse: I earn in crypto (BTC mainly), and sell what I need to pay bills and expenses a month ahead, and whatever's left, I send to my wallet.
3. Buying at a variable interval at a fiat threshold amount, which is probably what a lot of people do in smaller economies. That is, whenever they're able to save $100, then they buy Bitcoin. This I say because it's not always possible for everyone in all economies to save $50 or $100 in a month or two. And I know already some people saving up like this to buy BTC regardless of price, but whenever they have $100. The threshold isn't really arbitrary either, but you pay dearly in commissions and fees when buying below certain limits.