What a bizarre idea. The overall effect would be much better achieved, of course, by letting me cash in miles for iTunes credit, which would save them the trouble of building this whole expensive infrastructure (using software engineers who would be much better off redeployed on fixing all their other infrastructure...)
I can only assume that this is part of a longer-term plan. Perhaps they're obtaining the rights to sell digital content now so they can sell you digital content on the aircraft later. Why fly another airline and get entertainment for free when you can fly United and pay for it?