A meltdown of the US stock market will have a ripple effect that will cause economic distress world wide. It could very well push already distressed economies beyond the breaking point. Remember Venezuela? The Venezuelans have gone to great lengths to adopt cryptocurrency to replace their own failed currency. I'm not talking about the petro coin, but other cryptos that Venezuelans are using despite their government's attempts to prevent alternate currencies to flourish.
A crypto boom in the face of stock market crash really depends on how bad it gets for some countries. I would hate to see such economic disaster. If that does come, I would expect that mass adoption could take place when a fiat currency fails and there are little other options.