what are the useful applications for a 400GB micro SD card?
I'm not saying i'm not impressed, (if a little freaked out), I just can't think of what it would be genuinely good for, over say a 128GB card.
GoPro? Surely you'd be backing up / using that footage long before you hit 400GB (or is UHD footage much larger than i think?)
Music in a smartphone? really?
Media store in a media server / rPi? maybe.