Option to scroll through feeds horizontally
are you planning to implement horizontal scrolling through the feed groups? At the moment there are no maintained apps, where this feature is avaiable (old app is for example Palabre RSS, see below an old app screenshot). In my opinion this feature makes navigation the app a lot easier, if the user has grouped his feeds (just swipe left/right, no need to access the hamburger menu for switching).
While i have no programming skills, maybe i can help in some other way.