I did not say it was going to become impossible to buy 1 bitcoin, but with the coming years and judging with the track record bitcoin had set it will be much harder to buy one bitcoin in the future with the same amount used in DCA now, if it took 10 years to buy now it might take 15 years in the future so the only to keep at at 10 years would be to increase your weekly investment as was stated in the article.
With any work done diligently and consistently, I don't think it will be difficult for anyone to accumulate one Bitcoin for future investment. This is because it is highly influenced by a person's confidence in owning Bitcoin and never hesitating to continue buying without any reason. And if you're willing to dedicate ten or fifteen years to buying Bitcoin using the DCA method, you will have one Bitcoin, or even more. The DCA method isn't always measured by the amount of money you use each week to buy Bitcoin; you can use different amounts for each purchase in the coming weeks.
So, any investor who has started in the past few years and continues to use this method today will no longer be concerned about whether or not they can own a specific amount of Bitcoin. They will remain focused on their initial plan: to keep buying with the money they've set aside each week, so that the amount of Bitcoin they accumulate will continue to grow over time.