The only "killer app" for crypto*currencies* is being a payment method. Not counting speculation. This is what they are used for right now, but the scale at which this happens doesn't justify their current valuation (even after recent losses).
But is that a better experience than just using your visa? Nobody wants to wait at the cashier for 15 minutes to pay for their groceries, which is what has to happen if you really want the decentralized experience. Otherwise you really are just reinventing a worse, centralized payment rails. Volatility and wait times are features of crypto, not bugs, but they make for terrible payment experiences.
But is that a better experience than just using your visa? Nobody wants to wait at the cashier for 15 minutes to pay for their groceries, which is what has to happen if you really want the decentralized experience. Otherwise you really are just reinventing a worse, centralized payment rails. Volatility and wait times are features of crypto, not bugs, but they make for terrible payment experiences.
Writing that I feel back in 2021.