I want to use a one-time pad with a friend. That requires generating a fully random file that I then need to send to my friend (physically).
I don't have an Ethernet port on my machine to send the file on the wire, and I don't want to rely on weaker cryptography (WiFI, aes) to send this file (basically, everything is weaker than a one-time pad).
I also don't want to leave undeletable traces of my one-time pad on a flash drive.
So what's left is the actual screen of the device, provided I don't have any hidden cameras where I live.
I could use a hard drive and then shred the secrets, but nothing is proven regarding the actual deletion of the files, and QR codes are much cooler!
Did you consider using the front camera for bidirectional phone-to-phone communication? That could allow frame re-transmits which would increase the data rate a lot.