FWIW, Teensy will use similar copy code at startup. Supposedly NXP's boot ROM can do the copy to ram, but I can't figure out how to make it work. Looks like the mbed folks couldn't get it either. Not too surprising, since NXP's documentation is light on details and riddled with errors.
Paul, will there be an option in T4 to NOT copy ALL code to ram? I would like to keep most ram for data buffer and only copy FASTRUN code to RAM (e.g. FFT).