There is already an official Arduino ARM Cortex M3 board, the Due: http://arduino.cc/en/Main/ArduinoBoardDue

Teensy 3.0 afaik has some degree of support for Arduino IDE too. LeafLabs Maple has Arduino-style IDE too. And finally there is Energia IDE for Stellaris Launchpads.

So I'd say that the "Arduino for ARM" field is already quite contested, and I've probably missed some projects.