Hello,
Well, there is no such thing as standard HTML, especially when app like this one needs to store so much information (it's not just links and images).
But the good new is that the exported file is already a well structured JSON file that should pretty easy to parse and import into some other addon if needed.
I'm planning to add full synchronization with bookmarks so it will be possible in the future.
I would also like to say that as a 32 years "young" person I'm not planning to abandon this addon any time soon. Not to mention I'm using it daily myself and I can't imagine living without it :)
But it's good that you are thinking about backups!
Best regards,
Juraj Mäsiar