I like this idea. But you should be aware that it is easy for scammers to present a QR code to you with a fake amount. So you still need to trust the person that is presenting the QR to you.

Yes, I understand the problem. But when you pay via NFC Card you always will have this problem.
I experienced the following: In a restaurant, that accepts BTC via LN, the waiter types the amount usual without the decimal in his (Fiat) cash system (e.g.: he types "450 for 4.50 Fiat). So he wanted me to pay 450 instead of 4.50. When I payed with my own Lightning Wallet (Zeus), the amount was displayed on my device, so I discovered the error. With NFC, I would have had no chance. (aside from a limit).

Another idea is, to configure a PIN with the card, that I have to type in with the payment. Similar to a payment with Credit card.

You are right, even if you can trust the seller, mistakes can happen and with this improvement it would be possible to avoid it. I'll look into it and make a PR.