This is an interesting thread. I think a lot of your sentiments can be described in Ushiro Kenji's book "Karate and KI" (although often in terms that seem too mystical and inapplicable--could be a poor translation), and only mentions the exercises in Karate as a vehicle to explore this ki.
Gotta get it. Gotta meet him.
I think most of us had problems whether to approach this biomechanically or almost mystically by describing this stuff in terms of 'ki' or 'intent' or whatever (which is what Ushiro Kenji does a lot). I think the important think to realize is that controlling 'ki' or feeling the sensation of 'ki' in the other person is achieved through biomechanical correction--that is, the way we use our body must be first set before we can actually feel the 'sensation' of 'crushing' down our opponent to our feet. There is an actual way that that is achieved...
Well, there's two sides to that. For actual life-and-death fighting, the ki stuff has to be expressed through body and method and those should be only the most serious methods. We don't want to face a bear with nothing more than a plastic spatula. And there's that really informative video of the old ki master who can drop all his students with his ki, then gets punched in the face by the MMA guy. I would expect that ki is best used to help set up a technique or lead him into a position that you couldn't get him into with sheer muscle.
But as for feeling the ki, I'm starting on the other side and paying attention to myself and ordinary people around me, trying to observe which parts of their being are performing what functions. They come into the room and move around and talk about things and do things all in a mixture of physical, mental and emotional energies. Ki is involved in how they move their bodies, how they use their hands and eyes, how they use their voices, tone and pacing of what they say...
And I think by becoming familiar with the ki of people who live regularly and rationally, I can develop a sort of baseline feel for "normal" ki and how to interact with it.
But even to have this observing kind of ki, I have to have a mind/body/ki organization that allows my ki to be so calm and attentive.
The ki is easily affected by both the mind and the body. When we wake up in the morning, we may find that our body is rather stiff and slow. At the same time, we may recognize that this whole thing of "ki" does not seem so vivid as it did in last night's wine-fueled eager discussions. Then the mind has to do some adjustments to the body, unkink it a little, maybe stretch some of this or that and next thing you know, the ki is purring again. It won't purr when it's cramped up in a bent and rigid body. So work the body to make the ki feel comfortable and it will feel at home and will play.
So it's an inter-related combination of mental and physical things that support one another, that we're dealing with. Just the ki is not enough. Just the body is not enough. Mind and body is not enough. Mind and Ki only = idiot. Body and ki only may = prison inmate....
But to have that ki/mind/body organization for best living, we have to coordinate muscle, bone, fascia, mind, ki and breath to work effectively in nature. So for martial arts, we aren't using our whole selves if we aren't using all those elements. Technique may not be necessary, if you have enough power, but excellent technique, including all of judo, also contains important information and physical conditioning for serious situations.
Anyway, the body can weaken the ki through stiffness and cramped posture or vitalize it through movement. Certain kinds of movement can stir it up into turmoil while others can condition it and cultivate it. But the ki in the body flows through all the organs and tissues and vitalizes them. So if we don't move enough, the ki can't vitalize the body. If we move in ways that disturb the ki, we'll get sick. If we move in ways that condition and cultivate the ki, the body gets strong.
The mind can hurt the ki by refusing to interact with it. The rational mind rejects it and the ki is left to behave as it will. The rational mind cannot cure diseases caused by alienation of the ki from the self. Science cannot observe these conditions if they don't accept the existence of ki. They can only diagnose the physical or psychological manifestations of the severe inner alienation of the self. And it seems likely that if the mind can harm the ki in that way, the alienated ki can seriously disturb the mind as a result.
The proper relationship is like friendship between the mind and the ki. Think how frustrating it is to work with a computer program with a bad user interface. So if you're living without a proper relationship between the mind and the ki, it's painful. If the mind realizes that it has this powerful element of its own being, the nature of which is to support the will of the mind, the synergy can be fantastic. At any rate, it gives one the feeling of wholeness within himself, which instantly gives him a strong advantage over most people.
And a big part of the harmonization of the mind and the ki is their dual participation in using the body. Also, healing the body. The mind must use the ki to explore the body and recognize stagnations and weak spots and clear them to balance the whole body, which is the prime method of Chinese medicine. So the mind and ki together explore the fascia, muscles, bones, blood vessels, organs and nerves and condition them through movement and twisting, wringing, exertion of the extremities mediated through...the hara, where the ki can curl up and purr. Its nature is to run through all the nine crooked paths of the body and to curl up in the hara and purr.
An example of healing usage, in the thread on relaxing the shoulders, I wrote about my elbows being always somewhat bent due to having endured many badly applied elbow techniques over the years. I did have the result of opening the elbows fully through attention to muscular relaxation but they have not stayed that way. They are more open and I can put attention to it and open them further with ease. But what I've realized now is that those elbows are full of ki which has been held there for literal decades. And when I put just a little attention to letting that ki flow out of there, I feel a big response through my whole nervous system and my posture adjusts to a better form.
So the conditioning of the body can waken us to ki and the ability to feel it in others, but we will do well to learn at the same time to feel it when it is small and become familiar with how it works among normal people doing normal human things, learn to use our ki connection on that level of care and mutual help. Then we can understand the abnormal ki of an attacker as a distortion of the normal ki of a regular person and we will be better able to recognize it for what it is (though their outward appearance may be ordinary) or
move in proper relation to it.
Make no mistake, though: even recognizing his ki for what it is, a dangerous person is dangerous and more than ki swishing is required to survive an encounter with him. Read The Killer of Little Shepherds
to meet Joseph Vacher, the uke all aikidoka should have in mind when they practice. Then they will be doing real budo.
Best to all.