Just to visualize it a bit:
offering more payment options we would need more checkboxes - the UX would be horrible.
Perhaps instead of a registry - the QR code shows an IPFS or swarm hash and the content contains an json with the invoice. Then we would also get the message field that the burner wallet has. In this json there would then also be the accepted payment methods. DAI/xDAI/DAI over raiden/PlasmaSystemXY/…