Ellis,
I enjoyed reading your post a lot. To the extent that you've touched on the overall debate and the groups involved I think you have a balanced and respectful view of everyone. One of the points you make is close to one I have been attempting to make in this thread and others.
A rhetorical question I have been musing over is this: to what extent was Honma an aiki master? What sense does it make to describe his feat as an expression of aiki?
As you and Mark both pointed out, the term aiki wasn't used by Ueshiba or Takeda until many generations after Honma's day, so in a literal sense the question is nonsense, it is similar to asking "How many Marines held the line at the Battle of Thermopylae?" There were no "Marines" at that battle. Yet, US Marines feel a spiritual connection with the warriors of Sparta, and have taken the Spartan as an in-culture symbol of the virtues they aspire to. So a Marine might point to the valor exhibited in popular understanding of the events of the Battle of Thermopylae and say, "That's what we are, that's us."
Similarly, someone who is deeply committed to "aiki" might look back into history before the term was used much, find a story of some feat of martial skill and say "That's aiki." It would mean in this case, "That's the kind of thing I aspire to - to be able to be like that," or "to be able to do that." In fact the Honma story is really concrete - right out of the Daito ryu playbook. We could therefore talk about, not something like spirit or character that is in common, but an actual skill. "I train to develop a certain type of skill, which I call aiki. Here are some examples of great men in the past who have exhibited what I am talking about."
But here's another question - the person who recorded the Honma story called it kumiuchi. What did Honma name the skill he was demonstrating? What was the name of the principle he was exemplifying? What would he say to you if you went back in time and said to him, "Sir, that was an amazing demonstration of aiki?"
I think he'd ask you to repeat the question because he didn't understand what you were asking. Because the statement that he was demonstrating aiki is only true in some special sense. I think it is accurate to say it is "non-factual" since it cannot be proven or disproven.
I am not demonstrating, or even attempting to demonstrate, that there is any kind of "trademark" on the term aiki (though I do agree with Ellis's assertion that it is a type of branding). But I think there is a sort of line of appropriateness here that has to do with where you come from and what you represent when you make a statement such as "aiki has been practiced for generations going back to China and India." Because aiki is an inner secret of Daito ryu, and for Aikido, it is an all-encompassing, governing spirit that exists as a philosophical and moral principle as well as a martial skill. It is a particular thing to these groups, and some attention should be paid to how people inside those groups feel when it is applied to other things by people outside.
Let's say Honma bowed to the lord, and when complimented on his skill, stated, "Oh no, I didn't do that well at all. I have trained neko no myojutsu for many years but I am only starting to learn its secrets."
So what if someone emerged onto the scene claiming to be teaching "Neko no myojutsu." Let's say the person claimed to have trained in under several different IP masters, and developed his own system of training, and having read the story of Senguro Honma, he decided to name it "Neko no Myojutsu." Would that be okay? You can imagine how the lines would form - the usual suspects would decry that as ridiculous and flimflammy, and call this person a charlatan. Others would say, whatever, he has skills that we want to have, and we enjoy training with him. There are probably ways he could mollify the former group, and ways he could double-down and be even more polarizing and divisive, but at the end of the day, he has taken something that meant something very specific at one point, and turned it into a fairly hollow label, and applied it to his own thing.
The situation is more complex with the term aiki. In Daito ryu there are subtle differences in the place that term has in the skills and principles of the art as it is transmitted. I read it as more of an effect than a skill in my Daito ryu training. That may change, but I'd like to focus on what my Daito ryu instructors and sempai, as well as the training itself has to tell me about what aiki is in that context.
Aikido is actually a more complex situation. Personally speaking, in my training with them, my teachers have been vague on the subject of what Aiki actually is. What I think about that, is that they don't think it is appropriate to make a strict, explicit definition of Aiki, but to leave it up to we students to figure it out ourselves. And over the decades, it really seems like a lot of Aikidoka have taken the term to refer to things that are philosophical, ethical, spiritual, psychological, etc.
Reading about koryu for years and training it for about five years now has led me to believe that an integrated training system is more than the sum of its parts. You cannot break out some piece of a certain system and combine it with other pieces and expect to have a resulting skill set similar to proper training in each system. One of the reasons for this is that application of specific skills is of middling importance in koryu, you are training to be a certain type of person who responds fluidly, instantaneously, and uniquely to a stressful situation, but in a way that, upon later analysis, could be recognized as "exhibiting perfectly the spirit of" such and such a school. So a survey of 1000 martial systems across multiple societies and historical epochs that finds, say, a similar type of breath training, or a similar understanding of cross-oppositional body mechanics, is not really going to show you anything useful. It reduces to realizing that these are all systems created by humans on planet earth; they've all got two feet and two arms and similarly constructed skeletons and nervous systems. It doesn't say much that many of them get into breathing, or studying how their balance works, or what have you.
And that's basically why it is meaningless to say that Honma was an aiki master. And as for why it is misleading to "retcon" older martial arts as training "aiki," the point is that in those systems, the indicators of aiki you see are probably components meant to instill entirely different things, things that have been lost or are simply different. They are different paths. Everybody here is on their own path, why borrow a name for yours?