Concerning: One hand up, pointing upwards with one hand down, pointing downwards.
Tamura sensei does an exercise during warmup where he points one hand up and the other one down while focusing on his breading. I wish I knew what he was doing internally, but he does not explain that mutch (or I am just not able to understand his teachings). So with the little experience I have with Chinees internal arts, I try to open my body bit by bit from the ground up. The hand positions will keep me focused on opening my entire body to the sky and also to the ground.
Shimamoto sensei performs tenchi nage in a simular way, although he calls it the heaven and heaven technique (heaven in Holland and heaven in New-Zealand). He opens his body and you get sucked in. I also believe I have seen him finnish kotegaeshi nage with a simular stance as the one mentioned in the video of Ueshiba.
But again, these are just my observations and I dont really know how and why they are doing it. And as long as I dont get any answers that are more plausible to me, I'll stick to these.