Peter A Goldsbury
I think your Devil's advocacy needs to be somewhat stronger.
LOL! I was never very good at being Devil's Advocate.
Peter A Goldsbury
The point I am making is much simpler than the point you are answering by citing Nishioka on rei (with which I agree).
Takeda taught Daito-ryu kata (or waza, if you like) and charged so much per waza. I do not think he was the kind of teacher who would expose himself to danger by reversing roles and taking ukemi from his own students. Ueshiba, also, did not do this, but for different reasons. Of course, Ueshiba also expected his students to become better, but he expected them to show this in the skill with which they attacked--and also the skill with which they dealt with the reversal of roles--to put it in your terms.
On Takeda ... Do you think it mattered to him which role he actually assumed? IF the aiki skills are true body skills that are built within, then, would it matter if one was uke or tori? Even being tori, Takeda had the skills to make the technique go whichever way he wanted -- for most people. So, I find that it wouldn't have been much of a danger for Takeda to take ukemi from his students. If anything, I think that were the roles reversed, Takeda's students might find themselves in a worse position - having to deal with an attack from a "monster" of a budo man and not being able to handle it.
It's been my experience that people that have very good internal skills are going to do a specific technique no matter what I want to do.
Or, no matter who is uke or tori at the beginning. From that, I can't see Takeda really worrying about "danger" when training students.
As a teaching model compared to koryu methods ... I find myself contemplating the issue.