The design looks amazing, even though most people will probably have the device covered up with a phone cover. Also retina 2 sounds like i would need 3 versions of every image in my app which is getting to be a bit much.
To me, it's kind of like how the first people on Youtube now have millions of views, but good luck starting a new YT account today...
In Android you have to use 4 different density versions of your images to support the majority. And in BB10 you think about to differnt formats which have different artistic rules to them (you can't use the rule of thirds in a square, it doesn't work well).
So you should better expect screen size/density/aspect ratio differences in future or you will probably regret it.
I don't see why; for the edges, I think it'd look fine to just stretch the border-edge pixel out to infinity. All taps/gestures on the "sides" could be reported as occurring at the edge pixels. You'd need to modify your view-controller logic (to do something with all these edge-taps), but not your view.
Where possible I've moved my artwork flow from using PNGs for everything to translating PSD files into stretchable image slices and custom UIViews crafted in IB/Objective C via Core Image & Core Graphics. It's more time consuming at first but pays off in the end.