These guys are all supposed to be amazing predictors of the future. Who really cares whether payment data is transmitted via ultrasound, bluetooth, NFC, or over the wifi/cellular data connection? How does adding ultrasound to the mix shape the future, as all of these guys claim they want to do?
I blame the investors in this case more than Duplan. There are 70 people that wouldn't have been hired and fired if those investors hadn't written this apparently very immature 21 year old kid a $25M check for some hokey technology. Duplan clearly had a knack for communicating a believable grand vision, but little ability to deliver on it. Investors at this level - allegedly some of the most sophisticated VC's on the planet - are supposed to be able to identify people like this.