I think it died more because of its outrageous price tag. audiophiles would probably be willing to purchase a case that clips to a dac/amp combo, but the pricing can't that ridiculous... $600 for the dac/amp and $100 for a smart phone case??? let's be real... no one is going to buy that. price an inexpensive $30 or less case that can clip to your amplifier and smart phone, I can see a lot of interest. After playing around with rubber bands for the past few weeks, I can safely say that rubber bands are an extremely poor way to attach your dac/amp to your phone. I think some sort of velcro would be a lot better, but that is more reasonable to do on a DAP rather than a phone that will be unattached for the majority of the time.
edit: hell if oppo made a $30 case and clip for the ha-2 with the galaxy s5, I would buy it today.