This is very similar to how the early adopters of bitcoin when it was around $600-$700 must have envisaged bitcoin reaching $100k and now here it is and closer than ever.
 $1m is a whole lot but it's also possible for it to happen in the future. More investors can also act as a contribution to such increase in price. Meaning if it happens the market cap(price × total supply) of bitcoin will definitely be 21 trillion. That's indeed a whole lot.