now something that might be a great idea.. is creating an app which can embed a transaction in to a QR code on the fly.. (either a recieving app, or a payment) and let a QR reader read it off a phone screen.
No reason at all this couldn't be done. QR code, bar code, whatever, the transaction data could easily be embedded. Another thing that could be done (although this is much more risky unless done right) is bluetooth to bluetooth transactions. That way, older 'feature' phones don't miss out on the fun.