Re: supporting Amazon books. Isn't the entire point of the Nook platform to capture all the media revenue by NOT supporting other platforms, such as Google Play and Amazon? I don't think Nook Tablets are competitive against Nexus 7 and iPad mini. They should focus IMO on the low cost tablets, meaning sub-$150. The Nook got what success it had not by being the best, but by being cheaper. That said, Amazon and Google are determined to fight this one out, so there might not be a window of opportunity for much longer.
Going international will be very difficult, as in most of the richer countries there are already established players (like Kobo), and without the physical stores, is Nook really better than Kobo or Sony? Kobo has not been successful in the US for various reasons. I suspect that if B&N would face very similar challenges if they tried to go international.
B&N could also start buying and selling used books. Low-cost used books are one area where physical stores can beat online price-wise (if not selection-wise), because you don't need to pay for shipping. This is actually Gamestop's main source of revenue, IIRC.
Alternatively, B&N could reduce their book shelf space even more and become a gift/toy/game store that has a book section and a cafe.