It would require special equipment to make enough copies fast enough to make a worthwhile profit. A concert recorded at a decent bitrate is likely to be around 100MB in size. Copying 100MB even with USB 2.0 is likely to take 20 seconds. Since copying cannot proceed before the show has actually ended (for obvious reasons), you would need a massively parallel copying facility to be able to produce enough copies for the crowd yearning to get home but maybe willing to wait 1 minute to complete a transaction to buy the show. So it would probably be better to ditch the flashcard part of it and just let people sign up to have a copy of the gig sent to them via gmail or as a bittorrent seed.