I had such high hopes for this thread. But I guess the answer to "what is ki" varies as much as do the various experiences that people have had.
Looks like there's just too much variation in what has been experienced (and what has not yet been experienced) for this to go anywhere.
It is not nebulous or merely opinion -- but the categories typically used are ill-fittting. The traditional usages don't map into the same "boxes" of concepts that Westerners tend to use most frequently. Ki is not force, or energy, or movement -- but it has to do with force and energy and movement. It is empirical and demonstrable. Definable? -- yes, I think so, but you be the judge