In this thread
the discussion is around the race of teachers, and the question of whether it matters.
If we study aikido's principles, I will bet theories will come and go, and the practices which illustrate them will come and go, only to come around again. Then perhaps we'll discover the waza (and the underlying principles) really didn't go anywhere.
I'll bet the principles will stay alive forever. As far as the principles' transmission from generation to generation, my bet is also that this will become a more relevant to the teacher's cultural and technical background and influences.