I'm not sure I'm following your logic Mark. If it came from a Chinese source why not write it in Chinese, particularly since the characters are the same in Japanese? Are you suggesting Tanamo was trying to obfuscate a Chinese connection, if there was one, by using kana?
Also, if very literate Tanomo wrote down stuff and that stuff was passed on to Takeda, Takeda would have no need to memorize what he received, other than what the written stuff signified knowledge wise. Rather, he could just employ someone to copy his Tanomo writings when that transference was called for.
For example, we know that early students of Ueshiba received various Daito Ryu scrolls reflecting what they presumedly had been taught by Ueshiba. Curiously enough, this continued after Ueshiba no longer used the term Daito Ryu for what he was teaching. My understanding is that the scrolls follow a predictable sequence, reflected (to one degree or another) within Daito Ryu (big surprise). I'm guessing Ueshiba did not invent these scrolls, he probably copied (or had copied) his scrolls. His scrolls would have come from his teacher. We will probably never see Ueshiba's scrolls, for the same reason we will probably never see the Daito Ryu scrolls of the students that stayed within the Ueshiba organization. (Although the Daito Ryu scrolls of those that left the Ueshiba umbrella are publicly documented.) BTW, we are also told that Hisa asserted that the techniques Ueshiba taught his group were the same as what Takeda taught upon his arrival. (This would indicate a strong similarity remaining even after a period of Ueshiba's active avoidance of Takeda's presence and his assertion of teaching a "different" art.") Takeda picked up where Ueshiba left off. We also read that Takeda would be able to remember where a student left off upon his departure and would pick up from there after his return indicating that Takeda had a memorized sequence of instruction. Also, it seems that Yoshida Kotaro awarded Oyama Mas a Daito Ryu licence for umbrella techniques (I believe the techniques are listed on the licence. I seem to remember reading them of a photograph in the past.) It would probably have been "bad form" for Yoshida to have simply made this up, so they were probably copied from a scroll that Yoshida received from Takeda (Takeda probably had it made or told Yoshida to copy it himself and Takeda would seal it.) It is my understanding that this scroll exists in some incarnation of the the Daito Ryu curriculum. Finally, Budo Renshu reflects much of the contents of a particular Daito Ryu scroll indicating that either the scroll was patterned off of Budo Renshu or, more likely, Budo Renshu reflected the pattern of instruction that Ueshiba had received if not an actual scroll that he probably possessed. Of course of you are trying to avoid your teacher and strike out on your own it would probably be best to sever ties that could easily be traced to a past that wanted payment due.
Personally, I don't find the arguments that Ueshiba changed what he learned a lot that convincing. Rather, looking at the photographic evidence I come to the conclusion that much of what he did remained the same although he may, as indicated by the Manchukuo Demo incident, have had a preference for what he wanted to emphasize in his demos. Also, since I find a commonality between the Noma dojo pictures and his later demonstrations and Hisa asserts that what Ueshiba taught at the time is what Takeda taught as well . . . one might very well guess that Takeda appeared much the same (although there may have been a qualitative difference) and it is the later Daito Ryu practitioners that changed much in the same way that it was the later Aikido practitioners that changed what Aikido commonly appears as today.
Well, just spewing off the cuff . .
A question for you. In Stan Pranin's Daito-ryu book, there is an interview with Sagawa. In that interview, Sagawa states that the term, "aiki" was used before Ueshiba met Takeda. The interesting thing is that when Sagawa shows the notebook where the word aiki was written, aiki was written in katakana.
My question is why would it be written in katakana?
My wild, out of left field theory is perhaps because as we trace aiki from Takeda to Tanomo, we might find that Tanomo's Chinese connections were where these internal skills came from and because of that, Tanomo wrote aiki in katakana. Takeda, as we know, had an excellent memory (photographic, perhaps) and wrote aiki as he had been shown by Tanomo.