This is only slightly more future-proof than keeping text files on a computer. So slight, I'd argue the difference doesn't even matter. I don't see the advantages to this behavior over storing them digitally.
Digital index cards can be kept closer (on your phone, in your pocket, always), and arguably lower friction too, no? And plain text is pretty flexible too. IDK, I just thought the concept was strange - but if it works for you, that's great!
