I have over 300GiB of audio books from the National Library Service (NLS) for the blind. They're essentially an encrypted & protected MP3 that requires an authorized & registered NLS player.
Add to that another 200+GiB of audio books from other sources (audible.com, independant authors, etc) & I've just filled one of those cards.
Stack the e.books (mostly plain text) from places like Project Gutenberg & other sources, there's another 115GiB.
If you add my music collection to that (~40 years of ripping all my CD's to high CBR MP3's), then that alone comes in at nearly 750GiB.
Back when I could still see to enjoy them, I had over a TiB of movies I'd ripped from all my DVD movie collection plus all the ones I'd gotten as downloads from the places that offer such things.
A 512GiB card would be great, I'd love a box of them, but if you *really* want to impress me then give me a call when you've got a 512TiB card instead. THAT one might take a while to fill... because a USB3.0 connection can only saturate the databus for so long before the card catches fire.