1. Someone sticks a malicious NFC tag on one of those rental scooters that opens a malicious App Clip
2. The App Clip seems like it could be for the rental service
3. App Clip maliciously takes your money and runs.
Wonder how much something like that could become a problem or if Apple would be good enough about preventing/stopping it.
I assume Apple is hoping to rely on its curated app store to protect against that, but that is more of a social attack, so maybe we'll see it happen or something similar.
The "easy" fix is to make it obvious/hard to hide what the _real_ app clip should look like in-situ.
So this wouldn't work straight off as you describe. The NFC payload is just a url this url is sent back to Apple servers to load the App clip.
What could work is someone uses a legit App clip and hijacks the corresponding web site and places a malicious payload and tricks the App clip to load the malicious payload and tricks the user to tap on NFC / QR code and exploits App clip. Even then the last line of defense - sandbox needs to be circumvented.
Nevertheless, this is definitely a new attack vector and there will be exploits from NSAs.