Peter A Goldsbury
Well it was a 'secret principle', but I think you need to hold your judgment until you have read Shishida's comments about aiki.
I am trying to complete TIE 19 by the end of this month and this is why I have not produced a translation of Shishida's comments.
In a choice between me and TIE 19, I'd choose TIE 19 all the time.
We know that the actual word, "aiki" was in use in Japan's history. I believe even as far back as the Edo period? However, that's part of my point. If Tanomo learned the concepts and principles of internal skills from a Chinese source but it wasn't called "aiki" by the Chinese, then perhaps Tanomo used that word, "aiki" to describe the internal skills. Maybe he borrowed the Japanese word because it was close (equal to? I don't know) to the Chinese principles that he had learned but wrote it in katakana to differentiate or bring attention to it?
Ellis covered a lot of areas where Takeda learned his Japanese martial skills. Yet where does everyone say Takeda learned aiki? Tanomo. Why is Sagawa's father writing aiki in katakana and not kanji or hiragana? Why is it that Shiro Saigo made such a showing that it was reported as being different and when we look back, we find the link to Tanomo? Why is it that both Takeda and Ueshiba needed to be talked into using "aiki" in Takeda's Daito ryu jujutsu? Neither were keen, at first, to use aiki in the name. Why would someone want to put the actual "secret" out in full view of the public? Of course, we know that they eventually did and it didn't really matter. Hidden in plain sight, as Ellis says.
Ueshiba is, IMO, an anomoly. Something to be looked at as the exception. He completely muddied the water with his spiritual ideology that you can't use him as a source for tracing the history of "aiki" (just the history, not what it was or how to use it). And, IMO, those who trained under him are not exactly good reference material for the history of aiki either. Shishida's words not included as I haven't read them yet.
But, as you noted, katakana was in use extensively, so that explains the katakana usage. Or it could have been just to showcase the word. So, please, don't let me take time away from TIE 19.
Best to you, Peter.