If I could rift on this a bit... how about an app that can MITM NFC details for Android/Apple Pay in exchange for sats. You specify if you want to buy or sell sats in the app.

If you are selling sats, then you tap your phone to pay by NFC with Android/Apple Pay. The app finds someone buying sats and relays the exchange with the NFC terminal to the sat buyer. They authorize the payment on their phone as if they were standing there, and receive the equivalent in sats.

Lot's of thorny details about if you can MITM NFC for those apps and the sat buyer having their phone unlocked at the time. But I do think it's technically possible and would be a real game changer.

Because these are technically in-person purchases, the sat buyer can't reverse their cc payment and because it's Lightning they get their sats immediately. How to escrow this kind of instant payment is also tricky, but I believe a reasonable protocol could be worked out.

A big advantage is that it would not require tying up Lightning liquidity.