

my answer varies quite a bit depending on whether we mean tech that will be relegated to specific niche use cases and markets, tech that will no longer be produced at all, or tech that can’t be found any more, even used.
the first category could include a lot of things, like most of the other suggestions that have already been suggested here, but i don’t think there’s any chance of blu-ray discs or desktop computers being totally gone in that time frame. the second category will probably include small gasoline powered cars, at least in some countries. and the third category will probably include most standard incandescent or CFL light bulbs, but they might still exist in some niche applications.
i completely agree, though i hope that eventually we can settle on something like Cerabyte for long term archival storage.