I guess it depends on if you're talking about Bitcoin itself or crypto's in general.
I could see a situation in which a basket of like the top 10 biggest cryptos could make a good addition to an investment portfolio, particularly because of their unique price behavior, which could actually potentially reduce risk in a portfolio.
I could also see, as more billions come online, the need for some kind of cryptocurrency. But a lot of the explanations offered so far are unabashedly optimistically biased - in reality, they aren't wrong, but things just aren't so certain. In my opinion.
The optimism bias is human nature. I think if someone takes the time to really understand this technology it is so much bigger than just a currency we may or may not all get rich by holding. It really has the potential to alter the world in many fantastic ways.