Re: Kokyu development for Aiki in Aikido
Perhaps a good question or focus can be made about the use of the hara (dantien/tanden/One-Point etc.) in Aikido training (although the same principle will functionally apply in any art that seriously tries to 'move from the hara'). If you move from the hara, the hara controls the movement. In fact, the body has to develop to the point that "the hara IS the hands", in order for their to be true 'movement from the hara'.
So in effect, to cut to the chase, a lot of the various modes of training are really to build up and connect the hara to whatever point of the body is needed at a particular instant. The hara draws its power from the solidity of the ground or the down-weight of the body, the power of the legs, the hips, and the natural power of the hara, also. There's more to it than that, but the general statement is good enough.
The question becomes "how much hara control is used in Aikido?". As I noted in that post you quoted from, there's a valid question about how dominant the hara controls are in Aikido: Ueshiba appears to use more and better hara controls than I see in Tohei (this is a personal observation and is, of course, open to debate). The more dominant the use of the hara, the more a person gains actual "whole-body" controls and the purer the "mind-body" controls.
As I've said many times, there are many levels and gradations of the ki/kokyu skills and sometimes practicing one style will forever pattern you in such a way that you cannot switch over. It's a subtle but important point.
On the other hand, let's say for the sake of discussion that Tohei (and some others) indeed had a variant that was not as hara-dominant as Ueshiba's movement... how much difference did that make in their Aikido? Wasn't Tohei given a 10th dan by Ueshiba? Maybe the hara dominance is, for the purposes of Aikido, a difference without an important distinction?
If we circumvent the hara-dominance question, we still have to look at the question of hooking the hara to all parts of the body as the main (general) answer to your question, in terms of developing the skills. The parts of your question that have to do with the technique itself and handling of Uke's body are, to me, sort of separate issues. If the kokyu skills are 'pure', the handling of a given Uke will be done one way; if the kokyu skills or 'not pure' (or non-existent), the handling of Uke must be different, logically.
My 2 cents.