I made a very similar prediction just days before that guy said it. My prediction was $20,000-$50,000 by 2021. I'm leaning more towards $20,000 not because Bitcoin couldn't reach $50,000 if everything went smoothly, but because I think Bitcoin's share of the cryptocurrency market will continue to fall in relation to other cryptocurrencies. If that weren't to happen, then it could reach $50,000. But I think many great altcoins are yet to appear, and some of the existing ones, like ETH, will continue to mature and evolve, and potentially surpass Bitcoin in many ways. However, I still expect Bitcoin to remain top coin until 2020 or so.