Before implementing support for article collection files such as Kiwix files, we need to define how offline collections will be used within the app.
Some areas to think about:
Storage requirements
Download size requirements
Should images be included?
Do large downloads need to be reumsable? What happens if a 500 Mb download is interupted 80% complete?
Do users need to get Incremental updates or redownload the whole file
Wifi / cellular restrictions?
Security?
Prepackaged collections? or also defined by users?
How do users browse for new collections? Native? In app? Web? Where are they hosted?
Should wmf be able to generate collections? Edit them? What about volunteers? End users?
How do users browse downloaded collections?
How do users know if an update to a collection is available?
How do users know if a particular article is up to date or an update is available?
Related: these seem somewhat natural to mix with the reading list UI in the android app. Or another way to put it, these offline "lists" may compete or be conflated with existing reading lists, so it's probably best to use the same metaphor and augment the existing UI