In my opinion (feel free to ignore), focusing on the method rather than lots of recipes would be more helpful. However, if you have sourdough recipes for different baked goods like cookies, cakes, muffins, etc--the kind of baked goods people wouldn't normally associate with sourdough--I think these would be good with individual recipes.
Maybe a good detailed section on how to make a starter, preferably with more than one method: aka, here's a really simple/foolproof/cheat's way to get started, here's how they do it in these cultures, here's a good method if you're wheat-free, etc.
Also I like your idea of how to use up sourdough discard; I don't like the word discard though, it's such a waste! How to use up extra starter, how not to have any more than you need in the first place too. This I think would be very helpful.
The cookbooks that I really enjoy are a bit chatty; they are also older cookbooks--I don't know if some newer ones still employ this style as I only really buy secondhand these days. I do have some newer ones (still secondhand) that I refer to for specific recipes (mainly "ethnic" cookbooks) but there's a couple I will never part with because they are so much fun to read! Examples of the kind of chat I mean are menu suggestions (for example, an eclectic list of sandwiches, or what to pack for a picnic on the beach), anecdotes or little bits of history. I find it interesting and engaging to have this kind of extra content sprinkled throughout the book, though not interfering with the recipe layout. It might be distracting in an ebook though; I've only read your writing here on permies, not your books so maybe you have a different writing style (and go with your own style of course!).
I'm not particularly drawn to photos in cookbooks, but that's just me. Unless illustrating something very specific, I find them distracting; like the author/publisher needed to fill some pages to make the book worth printing. Other people may not agree with this.
I think you've got a lot covered and it sounds like a great project.