[zzo38computer]

Yes, these things can work. I think Plain TeX would be more likely to work better in fifty years than LaTeX; I use Plain TeX myself. I think TSV is also good.

I think PDF is complicated, though. (However, there are simpler subsets defined which omit some complicated stuff.) (If you really need to store the contents of a page, PNG might do.)

The SQLite version 3 database format is also unlikely to change I think and it is documented. (SQLite is also in the public domain, which also helps. You can avoid WAL and that other stuff if you want to ensure working in future, I suppose.) (If it does change a lot, probably it won't be called version 3, any more, I think.)

[cbm-vic-20]

I was using LaTeX in college back in the 90s; it was already ten years old by then. And since LaTeX is a macro package for TeX, it will run anywhere TeX can.

I agree, SQLite will live forever, thanks to its public domain status.

[rckoepke]

I do not think PDF will prove to be future stable.

[zzo38computer]

Yes, it is probably true. There are less complicated subsets, but using PNG to save the picture of the page might help better (although PNG doesn't used with CMYK or with extra separations). There is also DVI, which TeX uses as output, and it is simple so a program can easily be written to rasterize it or to convert to whatever other format the printer uses.