1 Bitcoin = $1,000,000 USD
21 Million Bitcoins = $21,000,000,000,000 ($21 Trillion USD)
One bitcoin for one million is possible, but it will take lots of time and luck, because everyone should use bitcoins then for this to happen
And i think that closest date that this could happen is not earlier than in 2050 and like i said only if we will be very lukcy