Hadn't thought about that. Not a bad idea. If a plane's installed IFE goes down for maintenance they could hand out diges in the meantime or (perhaps more likely) maybe each flight could carry a few diges on board to hand out to the unlucky passenger(s) who's backseat IFE screen is on the fritz. Only problem I see is that you still need to have all the distribution and training infrastructure in place even if its just a back up system.