Ok, so I've been to the seminar and basically the stuff in that article was just the surface of a much deeper and continuing study. The quoted article is really only an early attempt at dealing with a much more detailed subject. A lot of that detail was covered in the recent seminar and other training sessions and even more remains to be covered.
It's a lot to write about so I won't even try. Just thinking of it too much gives me a headache.
Suffice it to say however that Dan was right on some counts and that Josh's ideas on the use of hand blade and the serious issues in translation were also spot on.
A few points that may not be obvious from the article are:
1) The use of the word Aiki in the article and seminar is extremely specific. It relates only to a set of techniques in Daito Ryu that work from a grasping attack (this makes sense since the premise of Judo waza comes from grasping attacks, which is what the article was written to address). The word Aiki is not used to describe any internal mind/body processes, structural alignment and grounding principles or other unseen elements that may be used to apply these waza. My impression was that these skills were taught within the Daito Ryu syllabus but not under the name "Aiki" nor that these skillsets were a specific and separate curriculum per se. The demonstrations of this type of Aiki were also linked to specific known waza that included the name "Aiki," coming from Ueshiba's Aikido circa 1930 (e.g. Aiki nage as seen in Ueshiba's books "Budo" and "Budo Practice"). There may have been many meanings for the word Aiki in Daito Ryu. This article only addressed a particular type of Aiki as it pertained to counters against Judo.
2) The concept of straining hands makes more sense now and has nothing to do with Tori/Nage straining his hands or anything else. The hands that are "strained" are those of the attacker when they make contact with their intended target during a grab. Tori aligns his posture and projects or returns power into the grip by using his legs and spine as a base, realigning Uke's own structure in such a way that one cannot release the grab and is off balance. Balance is broken at the instant of contact and Uke appears to be frozen in space. When I took on the Uke role my hands were instantly manipulated and the force of my grab was realigned in such a way that my arm and spine locked up, leaving me totally off balance (floated) and fundamentally helpless and unable to release my grip. In a real sense the musculature of my hands were "strained" to the point where I had no more control over my grip to release it. So I can see how the translation to English could have given a different than intended meaning. An interesting note is that Shishida Sensei also consulted a member of Sagawa-ha Daito Ryu who indicated that this expression of Aiki was only the beginner stage.
3) I think the statement that these were "discoveries of Ueshiba" may also be off and may have been a result of Ueshiba's common history with Judo, Daito Ryu and possibly Kito Ryu. Again, English was not the strongest point of the article. The seminar showed that everything Ueshiba did during those days (around 1930 or so) was Daito Ryu. So yes Dan these were not unique imho but were expressions of Daito Ryu waza as shown to Tomiki and Takeshita by Ueshiba.
4) The question of whether Takeshita or others understood "Aiki" is not really a question based on the very specific context of its use in the article. If one did not understand it, one could not become proficient in Daito Ryu. From my discussions with the author and his research assistant, "Aiki no jutsu" was everywhere in the Daito Ryu syllabus, one could not become proficient in the system without getting a grasp of it imho.
5) The whole concept of Counters against Judo is based also on ma ai. Since Judo waza required a grip on ones clothing to work, Ueshiba would execute waza from the Daito Ryu syllabus that would capitalize on the attempt to grab and the grab itself. People like Kano and Tomiki could instantly create kuzushi on establishing a grip so the Aiki waza used would neutralize the grip's power at or before being grasped, while keeping a distance and position where one would not be vulnerable to Judo's sweeping techniques. Interestingly the "Tekubi okoshi" or "rising hands" technique used in Judo to cause kuzushi is also seen as a type of "aiki'.
This is part of what I got from the seminar in relation to this article. I'm sure there will be a lot of questions that I cannot answer, but there it is.
I hope this helps to add some context to the article. Like I said, based on the seminar that delved deeper on the topic, the original article does not say much. However I understand that an updated article or other publication with the new findings should be released, though I'm not sure if in English.