There are 59.4M millionaires in the world, yet only 21M #Bitcoin. Do the math. 
Discussion
the game theory exits here but truth is most are embarrassingly illiquid
That wealth is likely not in currency and stocks but in businesses, real estate, and maybe hard goods. Some of that will convert to Bitcoin, but only in about the 5-20% range. I expect from that alone, Bitcoin will hit $350k-$550k, and the rest of the way to and past $1M will be nations and states adopting it as a reserve currency.