There is definitely something internal in Judo in the higher levels. Just look at Mifune. Tim Fong and I were discussing this and he said that Kano would say that Judokas should focus on Tsukuri (setting up a good position for athrow) and then polish up Kake (execution of throw). We think that Kuzushi itself was 'higher' level and perhaps (this is what I think) all the dues you pay focusing on tsukuri would develop a frame from which you can understand the kind of Kuzushi that a guy like Mifune can effortlessly do.
Since my teacher was uchi deshi to Mifune, I got a lot more judo experience than I wanted or expected when I trained in his aikido. I definitely believe that aikido in general is much improved by judo experience. If nothing else, it gives a more realistic sense of what a real struggle a fight can be. And it lets the learner "lose" a lot. I think part of the weakness of aikido is that we never "lose" (in most aikido I've experienced) and so the teachers and senior people can get an over-inflated sense of their own abilities to avoid being caught in a real struggle. They tend to think they can't get into that kind of thing. It's good to find out early and not forget.
As for kuzushi, I think Mifune is a great example for what he "doesn't" do to achieve it. It's such a pleasure to watch him go and flip these huge guys and it's hard to see where he does anything until it's just suddenly done and uke is on the floor.
If we can say that judo uses internal skills (and I'll say some does, some doesn't), I think it must be in maintaining correct "frame" until uke makes a slight mistake, then being in shape, form and position to enter tsukuri with only a small movement. In other words, let him step into the spot and you just remain in good organization to capitalize on that. In particular, I worked a lot on the four major sweeps--osoto gari, ko soto gari, o uchi gari and ko uchi gari--looking for the moment where my simply being upright and relaxed would end up with me "fitted in" perfectly to his body to simply perform the reaps.
I think that level of work still amounted to external form, but it was moving more toward internal than anything I'd done prior to that. And I do think that a lot of what Mifune did was just that. Some guy supposedly said, "I'm younger, stronger, bigger and faster than you, so why do you always beat me?" and Mifune just said, "You take two steps, I take one." Which is what I was trying to accomplish with my foot-sweep methods.
As for Aunkai, lately, I'm thinking a lot about my few conversations with Ark in Atlanta, where he explained that his method was "choritsu" or "tuning" the body. Now I think of that (as he's sometimes said) as being like "tuning" a piano string. Or maybe a harp string. He tunes the body between heaven and earth and his technique is all about his own body's adjustment to energy that comes upon him from outside. If you touch him, you pluck that tuned harp string and you get the "ring" back into yourself as his body does whatever it needs to do to maintain its tuning between earth and sky. Of course, the harder you strike or pluck a harp string, the louder and more powerful the feedback will be.
I think it cannot be overemphasized that "internal" refers to the techniques happening within one's own body--not outside or between tori and uke. It happens inside "tori" and the effect on uke is because he is touching tori while tori makes the adjustment within himself.
And that is where I saw the big difference between what Endo showed in that clip on Atari and what Ark showed in the clip on Nyu Ryoku.
Best to all.