Wow, I'm really excited to hear Booxtor's statement on that. I understand that they try to avoid the high cost of replacing the display under warranty. But if they are actually not able to determine the reason of the defect and they even admit that, it's undoubtedly their duty to replace the panel.
I'm wondering, why Booxtor doesn't send it in to Onyx directly, if he doesn't feel enabled to decide whether or not this should be handled under warranty. From my understanding he should get a refund for the replaced display from Onyx, since their device comes with warranty from the manufacturer afaik...
Btw... "What would you do?" - I would definitely do the same you are doing now, write on this forum and make the mob complain mercilessly about the unfairness and the unfulfilled promises