Hi Louis,
Anything is possible with crypto. The fact that it will reach half million $ within 3 years is a bit optimistic, I must say. I won't say it will not reach as much as that but only when mining will become a pain in a butt to do so and the coins somehow are in control of worthy people. If a bitcoin will be worth 500k then it might become impossible to exchange with fiat currency.
At the moment bitcoin or any other crypto are still very far from completely replacing fiat currency. In London I have looked to see if any retailer does accepts cryptocurrency and I couldn't find one.
Unless big name start getting more interest in those cryptos there will be no significant rise in their value. If google would have started using bitcoin overnight the price would have risen to 50k at least. At the same time if the government would have been involved with crypto the price would have gone the other direction as we are back to were Satoshi started.