I believe the reason than Alan has not yet implemented this is because some transactions are too big to fit in a QR code.
Otherwise, yeah, it would be pretty handy.
The advantage of synchronous optical communications with sender and receiver in one place, as opposed to asynchronous messaging across time or location, is that you can display a visual stream of QR codes. Therefore, there's really no limit to the amount of data transferrable.
Cheers,
Rick