in your scheme though who is who ?
To avoid confusion, I maintain the standard terms as used in aikido. Uke attacks and gets thrown or locked. Tori/nage is attacked and throws or applies a joint lock. Ukemi is receiving nage's technique (e.g. ikkyo).
I'm trying to see this through the prism of "Nage is Uke" that Ellis puts out. So, if the traditional teacher is taking ukemi, and aikido's reversal of roles was intentional then the teacher (Nage) is taking ukemi forcing uke to recover and counter and get inside his technique.
Based on Wikipedia: in koryu the terms uchidachi and shidachi are used. Uchidachi ("striking/attacking sword") is the senior or teacher that attacks and loses. Shidachi is ("doing/receiving sword") is the student that responds and wins. The common way to map this to aikido is uchidachi = uke and shidachi = nage, meaning it's mostly nage that's training aikido.
However, Ueshiba and Takeda mostly assumed the role of nage, which implies that nage would be uchidachi and that it's mostly uke that's training aikido through ukemi (being thrown, being locked, absorbing forces, redirecting forces). This begs the question what and how uke is learning, hence this thread.
I can see how going with "Nage is Uke" can lead to the statement that "the teacher (Nage) is taking ukemi", but to me that's no more than a confusion of terms. I hope the above mapping with uchidachi/shidachi clarifies my point of view.