Some formats that are no longer usable in general, such as punch cards, were obsoleted consciously. And you might struggle to find a LaserDisc reader. Otherwise, we should be fine. Or am I missing something?
"The third disk here is the only known copy of the original design documents for Loom. It's an 800K Macintosh floppy employing a proprietary format readable only by a vintage Macintosh drive (thank you Apple). In preparing for this lecture, I obtained a dusty old Mac which had not been turned on since 1997. After reseating all the cables and boards I got it to boot and determined that the files on that disk are still intact and still fully readable. A few moments after making this happy discovery however, and before I could actually retrieve those files, the hard drive in the Mac crashed and died permanently. I'll recover the files eventually, but for now you'll have to rely on my failing memory for how Loom was conceived."
[1]: http://ludix.com/moriarty/loom.html (I transcribed the passage above from the video)
So imagine you have generations of digital files, converted from format to format to format. Why? Because software engineers are assholes who keep inventing new formats, for stupid goddamn reasons. A hundred generations from now, you'll be looking at copies of copies of copies which aren't just checksumable bit-wise copies but transcriptions, with transcription errors. If our descendants are lucky, all of those different versions will be preserved as well, but that just means that if you notice a possible transcription error, you'll have the opportunity to dig into two hundred year old character and file encodings to try to figure out what the original text was.
Which is not that different of a situation from trying to guess whether a scribe three copies ago misread the scribe four copies ago's atrocious f for a t.
"During the 1960s, the punched card was gradually replaced as the primary means for data storage by magnetic tape, as better, more capable computers became available. ... [P]unched cards were still commonly used for data entry and programming until the mid-1980s when the combination of lower cost magnetic disk storage ... made punched cards obsolete ..."[1]
Yes, I listed wikipedia as a primary source, deal with it.
I'm not sure if I'll ever be able to open them. I don't even have a way of getting them off the floppy.
But yes, I use it, both professionally and personally. Legacy MUMPS is not pleasant -- the VA's code looks like someone left their telegraph out in the rain -- but the language is astonishingly good at string-handling, mostly due to certain constructs that make it very hard to translate into normal languages.
Edit: On further consideration, I think we have to regard digital media and formats like a form of encryption (a simile, I don't mean this literally) which gets stronger over time. Time will bury extant evidence of what is contained on the media and how it is stored. Why should not make the information as explicit (plain-text) as possible? People in 800 years will still have to spend their efforts decoding early 21st century English legalese.
Compare and contrast: https://en.wikipedia.org/wiki/Domesday_Book#Custodial_histor...
But you need to avoid the mistakes that people have already made: using some weird format that dies, and then having all your data locked away in a semi-readable file.