Thanks for posting, Jun! I got something tangible out of it.
I love Iwama aikido, and I've always liked watching demos from Feder sensei. But I still get worried about whether uke is choosing to play along, as opposed to having little to no choice. I like seeing the latter (Ikeda sensei, mentioned in the excerpt in OP, is along those lines).
That being said, that uke's ukemi was inspiring. I've heard of soft-landing breakfalls, but this goes even further-- he turns a breakfall into a kind of a roll (see 0:08 and 0:12 in the vid). I wasn't sure if that kind of breakfall was a great way to fall gently, or a great way to hurt your shoulder or spine.
But I figured don't knock it till you've tried it:
Now that I can kind of do it, I think it feels much less precarious than it looks. But not sure about higher force loads (like if I am thrown hard, or fall from full standing position). Also not sure if I can easily do this without preparation, when my balance is taken-- in other words, if it really works. At least it doesn't hurt anymore, now that I can kind of do it. It did hurt to learn it though.
The way I did it, it looks like a forward roll, but note that the lead arm doesn't even touch the floor after all. I deliberately set it up to look like I would do a regular forward roll on my right side. But then, I stopped my right arm from being used at all, and instead used my left arm like in the video. I continued the "roll" all the way to sitting, but you can see my landing is left side down, like if I was taking a normal breakfall from a kotegaeshi applied to right hand.
If I had instead done it wrong by just changing it at the last second to a left-side forward roll, you would see my back to the camera at the end of it, rather than my front as shown here.