Adding at the end:
"So in conclusion, I’m going to go against my source and predict an indefinite lifespan for current ebook formats (barring some unpredictable random occurrence)."
I've done some digging around, and all the media file formats in use on general purpose computers that I can think of offhand, from GIFs to PDFS, are all less than 40 years old -- mostly a _lot_ less. Now you could _claim_ that SGML is older, dating from 1960, but no one uses that language; they're all using one of SGML's bastard children or grandchildren or great-grandchildren, and in any event, you'd have to do some character translation to get from a 1960s era file to a 2013 era file (you might be trying to read EBCDIC on a magnetic reel, type of thing, when you're accustomed to ASCII on a flash drive).
I guess I'd put it this way. A new consumer product era -- for ebooks on ereaders -- started in the mid 2000s. The 20-40 year rule says that the format of those books will be largely out of use (all but a tiny fraction of new comparable items will be sold in a different, incompatible format, and you'll have trouble giving the old ones away, altho you should be able to still pick up a compatible device to consume the item in question, used and cheap if not free, the way I bought a portable 8 track player for $2 at a garage sale in 1986 or so) by 2040. I can't see _now_ what the replacement will be, any more than in 194x anyone was thinking about CDs.
But I kinda think there will still be a replacement. And at 71, I'm probably gonna have to figure out how to use the damn thing, which will only be harder as my eyes age.
ETA: I feel like my perspective is clear enough that I should not have to say this, but I will anyway. I do NOT have a problem with formats becoming obsolete. Is it irritating when I have to go dig copies of stories I have written off a decade old iMac and figure out how to strip off the Smart Quotes and deal with line break issues and blah blah bleeping blah so I can post them on my website? Yes. It is irritating. But it does not make me want to give up. It reminds me that as time marches along, I should be migrating the things I care about along with me, and disposing of that which has no future value to me.
And trusting that, should I need to go back and strip those SmartQuotes off, I will be able to figure out several ways to do it, one of which will strike me as least inconvenient, and I will just grind my molars and Get It Done.