From the article:
Accordingly, our long-term price target for Bitcoin is approximately $400,000 per coin, based on taking the market cap of all the gold in the world and dividing it by the number of bitcoins that will ultimately be in circulation.
I wish he would state what exactly "long-term" means. If Bitcoin continues to survive over time then it's price will likely go up over the long-term The question is: Will it reach $400,000 in my lifetime?
It depends how old you are

Every price could be possible once papers will not be used and the main fiat is removed. In other terms, once bitcoin will be adopted worldwide and satoshi become the actual dollar