It's easier to look at total market cap instead of the actual BTC/USD price.
600k per coin would equal $13T market cap, which is almost twice the market cap of gold itself.
Not impossible, but it will definitely take longer than 2 years. Every time the market goes up a lot, early hodlers will tend to sell some of their holdings, bringing the market down again.
I'm sure no one thought gold would come here to its present value from the first days it was found, and would leave a lot of FIAT money behind. I cannot say that it overtake the current value of Gold. But why wouldn't it really be possible?