Thanks for the suggestion. As Lostinlodos says, we’re looking into this for both Android and iOS. On Android, we’ve offered a ‘Save to SD card’ feature for a long time - which, I think in recent Android versions simply saves to internal storage. We save it in a ‘kindle’ folder which the Amazon Kindle app on Android looks inside for ‘side loaded’ documents. That still works. It gets loaded in the Kindle library. But on the device it’s just a MOBI file with a cryptic filename, so not really intended for the user to access directly.
Offering a regular epub/mobi download would be useful. So we’ll definitely see what we can do here.