If nothing else, I would imagine Shioda, Tomiki, Shirata, and some others were chasing the aiki they felt from Takeda. Since that aiki was a rarity, there weren't all that many teachers to turn to and it was a very closely guarded secret. Any avenue to get better was worth approaching. Shioda was very lucky to get to train with both Ueshiba and Kodo.
I don't think it is that simple Mark. And I definitely don't think Shioda, Tomiki and Shirata were chasing the aiki of Takeda. They were chasing the aiki of Ueshiba. IIRC, Shioda never met Takeda. There were "others" as you mentioned, but some of them did not like Takeda much and chose to train with Ueshiba instead. Admiral Takeshita was one of them.
Shioda's training was mainly with Ueshiba. While his training with Kodo was not extensive, it was what was covered, what he said about Kodo's skills, and how it changed his own practice in a different direction that is of interest. This ties back into your thoughts on exposure, and training times of Ueshiba's students and what they did or didn't get. How,does that relates to Bills own ideas on Ki in Aikido?
Time in- V exposure to correct practice:
Bill's comments, were you to hear them fleshed out, is that most people are not doing aikido correctly. That they are pursuing waza and external movement instead of ki and so they end up missing aiki. There is no amount of "time" that will change that. Change requires a shift in thought and direction; with MA that can come as an epiphany or from exposure to new schools of thought..
You have heard similar things yourself-now from other teachers, not only in AIkido, but other arts as well. How many times, in different places, have you met teachers who told you the information they just received, ( in some very short time frames) and the training they just encountered has changed their aikido forever; the way they see it, teach it and want to train it? You have heard people say they will NEVER go back to doing aikido the same ever again.
How is that any different, than:
Ueshiba saying Takeda "Opened my eyes to true budo."
Hisa meeting Takeda after training with Ueshiba and saying this was completely different then Ueshiba (at that time)
Shioda meeting Kodo and what he said to him, then his aikido changing, with him even copying the moves he is famous for.
Is it so far fetched to think that even a short exposure would change someones goals and practice forever?
And what did that change always revolve around...the pursuit of aiki.
So, as Bill noted,"Ki in aikido"
is not a concept that produced a reality in movement and delivery from everyone who claimed to have it. Hence, the ki wars that happened. Now circling back, that seems to be changing again....through exposure.