Either way you would have to manually copy then the pubkey then from one place into another to set up the delegation.
But most clients will never implement delegations, so this is a non-started to me :(
Discussion
I really like QR codes, I would just never put a private key in one as it makes them too easy to steal.
If I maintained a client I'd keep it open as a possibility because delegation removes the need to copy private keys between devices. No longer need to copy keys in any form, could be made to work with a hardware device, and the cryptography is simple, so why not try it?