So would a $2.5 million BTC actually be more like $250,000 or even $50,000.... I just can't see 50% of the world's population being millionaires.
If you knew the global population it is around 7.8 billion and if you estimate the number of BTCitcoin investors i do not think you will see more than 100 million users investing in the market and in that how many users will be holding more than a BTCitcoin. So even if you speculate that the price of BTCitcoin crosses a million dollars you will not see half the population becoming millionaires 
.