My use case is similar to davidfor's, I often have two or three "now reading" items. As a Nook refugee, it's sweet how Kobo shows a group of recent reads instead of just one.
So to me, the ideal solution would be TWO screens, both with five chronologically-sized covers. One would be "Currently Reading" and the other would be "What's New."
Doesn't matter which one is "Home," that could be a user preference if it's not too deep of a choice. Ottdmk's point is well taken – having the new stuff always up front may indeed be best for many users.
It would be important to make these two screens visually distinct, not just differentiated by a small label in a whispy font. At a glance, it needs to be very clear whether the user looking at New or Now.
Perhaps "Home" could be a carousel-style layout: the home button gets you to New, then a left/right swipe gets you to Now. Whichever one you're on, the other is just a swipe away. Or the home button could take you to whichever was used last time.
(Likely not feasible to animate this, but just the left/right, A/B context would be enough.)
Displaying five differently-sized book covers is terrific. I'd just like to see it applied to both "new" and "now" scenarios.