alt Hacker NewsWhen the original application is open source, its format is public and anyone who wants to create a converter to another format can either use the original code or inspect it to see how the format works.
When the format is proprietary, you get a blob of binary data that you have to reverse engineer through guesswork, made orders of magnitude more difficult if the original service isn't even available anymore.
The problem reminds me of pdf, the format is well known, there are tons of third-party readers, but they all glitch somewhat differently.
Also PDF is turing complete.
Modern rich content formats are hard. Open formats solves only small part of the problem.
I think the universal interchangable format is static HTML.