Normally, a two finger pinch on an article returns the user to the browse page for the collection the article is in. Alternatively, the user can tap to reveal the title bar, and and the name of the collection is tappable in the upper-left corner of the screen.
However, if you have buttons that link between articles in a collection, and the user taps one of the buttons, the name of the collection in the title bar is replaced by "Back", so that the user can return to where they came from. But if you've followed several "jumps" this way by clicking on 4 buttons, for example, the user needs to tap "Back" 4 times before they can tap on the name of the collection to return to the browse page. Also, when a link is followed in this manner, the 2 finger pinch does nothing.
It is critical that a folio-type of experience still be possible in DPS 2015...and this can ALMOST be done simply by creating a collection with multiple articles. But this behavior really makes a collection consisting of linked articles very difficult to navigate.
Nate, I think the "back" functionality is important. But there also needs to be a direct way to always return to the collection. Perhaps include both the Back button and the return to collection button in the title bar, or at the very least make the 2 finger pinch always return to the collection, even after a link has been followed.
On second thought, I suppose this is problematic when you have an article that contains a button that points to an article in a different collection. Maybe a solution would be to enforce the current "back only" functionality if a button has navigated away from the original collection, but otherwise implement one of the solutions above if the navigation has taken place within a collection.
As much as Adobe is promoting "article-based" publishing, and I believe that has value, I'm convinced that many customers will use the folio-like behavior of collections as an interim solution and as a way to sell back issues. So there needs to be rock-solid, simple functionality for this. The migration tool is awesome for how easy it makes this. If you can make the user experience straightforward, we'll be set!