I didn’t make it to Brickvention this year, but Adrian O’Hagan did, and sent me this photo. It’s a Lego Myki reader… and on the back of it is a Metcard reader.
Adrian says when a Myki card was presented it beeped and displayed a balance (which may or may not have been the real balance; I’m assuming all the information on the card is encrypted). The Metcard version would take a presented Metcard, pretend to read it and then spit it back out again, just like in real life.
Adrian notes: “ironically the metcard worked without a hitch, but the myki was a bit buggy. Not sure if that was by design or not ;-)”