500.000 USD seems to be on the optimistic side, but it would not surprise me if the price would got to 10k all of a sudden when bitcoin is stable. With that I mean no more fight about who controls bitcoin, but a true community consensus. Many investors would likely jump in.
I think calling optimistic to someone expecting the bitcoin price to reach 500,000 dollars is an understatement, most of the world economy will need to move through bitcoin if bitcoin is ever going to reach that price, and even if I am optimistic about bitcoin, that is not going to happen anytime soon, and if it happened, at that time its value in fiat will be irrelevant since bitcoin will be the point of reference at that point in time.