It's not as great of a prediction as you'd think; namely, if you use the value of a 2017 dollar then $1mm is a lot, but if by 2020 $1mm will only buy you a loaf of bread, then his prediction might be true but is meaningless.
What's important is that McAfee has bet his own dick (which we will just have to ASSUME he still has, or is a meaningful sized meal) on hyperinflation of the dollar, essentially. This is where he runs into some serious problems, bc there's no great evidence the DE-flation of this 1999-->present depression is done yet-- in terms of deflation vs hyperinflation era.
So we think he's still nuts, but if he's right on hyperinflation then $1mm isn't a big deal for Bitcoin.
Pretty far stretch to imagine that $1 million USD will only buy you a loaf of bread just 3 years from now. Not impossible but also not likely. I get your point though. If the dollar doesn't buy much it's not saying much. We will have a lot of other things to be worrying about if $1 million USD only buys us a loaf of bread in just 3 years time as opposed to what Mr. McAfee will be doing with his anatomy though. ;)