Right now hardware/arduino/avr/cores/arduino and hardware/arduino/sam/cores/arduino contain redundant files, for example Print.cpp, WString.cpp, etc. This makes maintenance complicated, since changes on one won't affect the other (even when those changes are platform-independent), so the developer will have to make the changes on multiple files (and something tells me SAM won't have the same attention as AVR). I think it would be a good idea to unify them so that all platform-independent sources are common, and then each derivative has a small set of platform-specific sources.