Uki Otoshi is the forgotten throw in the Uki Waza of Tomiki Ryu Aikido. Uki Otoshi is a floating technique where Uke is thrown off his toes while moving forward. I believe Uki Otoshi and Hiki Otoshi are identical techniques, except in Hiki Otoshi Tori kneels to the ground during execution to the technique.
Judo - Uki Otoshi
The reason I bring this up is that I believe many people mistakenly label their Sumi otoshi - corner drop, when it is really a Uki Otoshi.
Let's look at these guy's again. It is a great throw they have - but I believe it is an Uki otoshi rather than a sumi otoshi. You see during the final execution Uke is thrown forward, rather than towards the corner that defines the throw.
See...uke falls forward exactly like Uki otoshi. All the balance breaking stuff should not be part of the taxonomy of the throw, or rather it's labeling.
Now compare angles to this sport Tomiki guy. His execution is clearly towards the back corner. This is the angle of a Sumi Otoshi - in my humble opinion.
So this is some seriously picky Aiki nerd stuff. But I think returning to the principles is important and I believe is why we have the 17 kata in the first place.
So let's clarify what I believe an sumi otoshi to be further. At the moment of tori's center drop - it must must towards the outside corner. Uke of course has choice's. If uke turns into the drop, Uke can take an air fall or roll out. If their system locks up, then a backfall happens. The important part of defining this throw is the relationship between centers at the moment of execution.