Peter A Goldsbury
The point of this chronology is to suggest (1) that the spiritualization of his training would probably begin in Period 3, with Omoto and his chinkon / kishin and misogi training, (2) that it might be possible to map some sort of IP training right from Period 2, if not before, and that (3) the ‘Rites of Spring' taught to Hikitsuchi in Periods 6 and 7 would be the distillation of intensive personal training of some sort (including what we would call IP), right from the beginning. This training might also include plenty of trial and error, and also include Ueshiba progressively becoming aware of the strengths, weaknesses and pitfalls of this training. Did he ever have a teaching plan?
This is helpful. For example, the chronology helps Illustrate how some but not all elements of what would become the Rites of Spring ended up in Tohei's documented and preserved aiki-taiso.
Would you consider mitori-geiko a teaching plan? I suppose even within that question, it depends on whether or not he primarily intended to teach by example vs. viewed students first and foremost as personal practice tools (I have no idea within that continuum where he placed his intentions -- fortunately, there are still people alive we can ask for input). History shows that the power was profound and distinctive enough that it compelled the "perceiving" group to go all out (and literally "out" of the art, if needed) to develop their respective tanren to unlock that power within themselves. Ellis, for example, provides in Hidden in Plain Sight
wonderful details about Ueshiba's shugyo. Ueshiba wouldn't be the first or last Asian teacher who would expect a student to similarly find his/her own way and get immersed in it.
You've pointed out that aikido is not like koryu bujutsu, to which the question of maintaining what's "pure" might better fit. (I study Hakkoryu, which has a decidedly more koryu flavor, despite being a gendai budo contemporary to aikido with many common characteristics.)
So if finding something "pure" within aikido is difficult because of its progressive, eclectic nature (spelled out in your timeline), is there something that's a constant? Of course, that should be aiki. When all of the discussion (i.e. debate) regarding IP as aiki began to simmer toward boiling over during the latter half of the past decade, I never thought I'd view folks like Dan and Ark as part of a pattern of outside influence that has been instrumental to preserving a key aspect of what is central to what makes aikido, and individual aikidoka, "strong" in the general, non-abstract sense. Again, we have hombu and non-hombu senior aikidoka who know this is an inner-door quality inherent to the art, and are acknowledging its presence in the students of these modern teachers -- often times without having encountered the teachers themselves. But what you've laid out in this thread, along with the historical stones others have turned over, point to just such a pattern.
The difference during this historical cycle? This time there are express teaching plans, and there are codified pedagogies via which the power perceived in aikido can be systematically achieved.