That would indeed be interesting  

But I think the problem is less likely about volatility since most popular payment processors enable instant conversion of crypto to fiat. Most probably the biggest setbacks would be btc not as fast as fiat payments and most would probably still use their fiat most of the time for spending.

As a consumer, I'm also worried about the future. IMO there is more friction with crypto compared to fiat in the eyes of regulatory bodies. As it stands,  these policies are bound to get stricter over time and it wouldn't be unthinkable for big e-commerce platforms to be hit.