As someone who has used several cross-platform frameworks (Titanium, Cordova/PhoneGap, investigating Xamarin), I have a question about going "full native": how do you handle shared core code? Our app has an engine that drives the business logic, and the cross-platform frameworks have been useful because we don't have to deal with modifying the core codebase for different platforms [0]. Is it possible to create platform-agnostic libraries that can be shared?

[0] Despite the many claims of "cross-platform UIs," we have many cases in our UI layer of doing different things on different platforms.