How can you challenge/response with a QR code?
Or a mag stripe? Maybe it could work with sonic payments, though I have no idea how they work (never heard of them until now) so who knows.
Not sure what the point was of the researcher suggesting a remedy that's clearly impossible. The whole point of Samsung doing their mag stripe thing was to allow Samsung Pay to work with old swipe only readers. If they were going to be upgraded to be able to respond they might as well upgrade them to do NFC.