I've been really intrigued by these arial backfalls. Most of the ukemi I learned consisted of the straight backfall (as in squat, roll back and up onto your shoulders), the side fall, the forward roll, and the flipping version of the forward roll where you basically slam into the mat, and maybe the front fall where you land on your forarms and you feet kick up into the air and you land like you're sort of breakdancing.
Which seems to cover most of the bases, but I'm sure that these aren't totally unnecessary. The regular backfall seems to suffice in many instances, but there have been times when both feet cleared the mat and I ended up landing flat on my back which nearly knocked the wind out of me. (Someone caught me in a good ushiro ate a month or so ago which prompted that sort of fall.) I wonder if this sort of rolling approach would take away a lot of that flat impact.
I wonder if the sort of falling we do stems from a judo background (since both Mr. Tomiki and Mr. Geis both came from a judo background), where uke tends to remain attached to (and controlled by) tori during the fall, as opposed to aikido where uke can very literally be caught out in space all alone after a throw?