that would be really useful.
And although I understood the analogy, I still don't get the technical aspects of why you can have 1,000 devices that are all the same but they each need a different file. I'm used to building Windows computers, and you can use the same image repeatedly for multiple copies of the same type of computer.
I'm also wondering: why can't anything be installed straight from the SD card or even USB when a device is bricked? How does Asus do it when they fix people's motherboards?
Assume that it is a string of lower-case letters (good chance that it has numbers, capital letters, and all sorts of fun stuff). A two-character signature has a space of 26*26, which is already over 625 keys. That number scales hella fast when you add more characters.
Asus will fix your tablet by either replacing your motherboard completely (more likely), or they may have the NVFlash keys for your device by its serial number. However, since your bootloader is unlocked, and they will have your serial number on file as "unlocked", they may just refuse to repair it outright. Surely, they will refuse it for a warranty repair, though I don't know if they will even repair your device for money.