I tend to agree with Mary's and Cliff's view that the aiki ken/jo kata should be martially sound in order to adequately inform the taijutsu efforts. I would not limit martial efficacy to partner interaction (ma-ai, metsuke, etc.) but extend it to how the weapon is wielded (transfer power to the hands and out to the contact area), the role of waist vs. hips, weighting, etc., as all this translates to body arts. That said, my main issue with some of the aiki weapons I see is that the way they wield the weapons, move, cut, etc., is in direct opposition to how I understand aiki should be manifested or trained, not to mention being martially unsound (based on my experience). I can entertain the idea that "this [aiki ken/jo] is not supposed to be sword fighting", OK, but then I wonder, how is doing weapons like that going to help me get aiki?
I have no idea. I came to aikido from other martial arts, including shindo muso ryu jodo, so I will never have the "pure" aikido perspective. I think I do a pretty good day-to-day job of emptying my cup, but it's true, there are certain aikido concepts that I can only understand from my experience with weapons. Kokyu is one of these. We never used the word when I was training in shindo muso, but it seems to me that when people talk about "kokyu", they're talking about the...what to call it? tension? mutual presence? I hate to say "connection", because that gets people thinking right away about a physical connection, and in jodo, the moments of actual physical connection were mostly fleeting -- yet for the entirety of the kata, there was this thing between you and your opponent, and God help you if you screwed it up.
And "blending", that's another. We never talked about "blending". We talked about taking openings, responding to techniques, etc. I think the martial roots of aikido must have had this in mind when talking about "blending", rather than some ethereal let's-all-dance-together-in-harmony becoming one with the universe. But I don't have any idea if any of that is true.