You are wrong. AROS sources have always been more or less M68K binary compatible (even all library sources have complete 68k register parameters defined!, most public structures are 1:1 identical) It is actually designed for 68k from the beginning.
No one was interested to do following (until Jason appeared):
a) to make it actually compile correctly (that was very big task)
b) add low level kernel code (task switching, interrupt handling etc.. Not an easy task either)
c) add missing hardware drivers (mouse, keyboard, graphics, disk etc..) I have done most of these.