Re: to see "office" applications go away - pages are so last century
I'm quite a lot more confident of documents authored in markdown being useful in 75 years than any particular "office" format. Agree though that at least ODF seems to be heading in something of the right direction. I'm just not confident that a volunteer team can keep useful presentation software going for such a complicated specification in perpetuity. We'll see.
(One of the) points about corporate wikis and web standards is that it's a different and interesting twist on longevity. The storage format isn't generally described at all, and the display implementation doesn't really matter, and can track whatever web standards exist at the time. Point is that the entire document repository is online and live all the time, so changes in the back-end ought to be applied as they go, fixing incompatibilities as they arise. As everyone who has ever had anything to do with software knows, there's a lot of "if" in that plan, and it does rather depend on your vendor staying alive, which I'm sure they love.
I used to think that (La)TeX was a good basis for document longevity, what with being open-source and readily available, but it's currently aging poorly, IMO, and interacting badly with Unicode, so I'm no-longer so confident.
Reckon I'll stick with unadorned ASCII, or perhaps markdown. Maybe troff?