publishing use cases for persistent storage for bundles

We hope that bundles (most likely unsigned?) would be used for distributing publications, such as ebooks. We do hope that some sort of persistent storage would be available on the user's device. Here's a list of a few use cases, created by @jaypanoz:

• storing a list of quizzes/games which have already been done so that it doesn’t reset every time you open the publication;
• storing a list of values for a checklist so that you can automatically save the progress;
• saving a drawing in a canvas – although this is a little bit of a hack as it can only store strings and you must base64-encode it on the fly… but when you’ve got nothing else, it does the job;
• saving the current position in an overflowing element since mishandling can happen (turning the page accidentally, which loads a new resource and resets the state of the current one);
• saving the origin of a redirection to easily get back to the previous page if needed – yeah I know there’s a “previous button” in the bottom left corner but sometimes it takes years for users to discover it;
• more generally saving any information you’ll retrieve later, which can go from practical things like the examples above, to technical things like storing the results of a feature detect requiring to create an element, test its styles and remove it, which will cause a repaint (there are obviously different strategies to deal with upgrades or invalidate those results whenever needed there).

No file, test, or entry point is identified. Start by reviewing the listed persistent-storage use cases and the web packaging format context, then determine what concrete change is being requested. Done would require an agreed scope and a documented way to support the relevant bundle use cases.