I've been getting them a lot lately in resistive practice, but I had to change the set up a bit from the forms we do. I would really like to see one done in a shiai.
As Larry said it requires very good posture and ability to send power or weight through your arms and keep the uke pinned on one foot. It mostly happens tenkan, not irimi. Most ukes/tantos in competition feel the push on the elbow to set tenkaigotegaeshi up and will pull the arm back in to the hip and try to square back up with you, which is why I to tend try sumiotoshi or aigame ate coming off tenkaikotegaeshi. But it is possible to spin back to tenkaikotegaeshi off maeotoshi and that's a nice combo if you can swing it.