The only question is how to handle SysTick. In Teensy 3.0 I replace the handler with one that that duplicates the Teensy 3.0 functionality and the RTOS needs.
I want the standard Arduino functionality to continue to work and have the option for a few high priority tasks and ISRs to use the RTOS functionality.
I see the issue with SysTick, i've found the following solution to avoid code duplication:https://github.com/arduino/Arduino/blob/ide-1.5.x/hardware/arduino/sam/cores/arduino/hooks.c
you just need to define a function called:
that overrides the empty sysTickHook. If you return 0 the Arduino's handler is runned afterward, any other value instead prevents it from running (I don't know if this could be useful for something but its for free).
I understand that full preemptive RTOSs are not appropriate for most Arduino users but a few advanced users want the functionally of a full RTOS.
Until the changes needed are so small and doesn't affect anything, IMHO its worth trying. Of course, don't expect support for more advanced stuff about RTOS... from now on you're alone!
(but I'm curious to see what you can do it