In my instructor's way of thinking, it isn't that one has the wrist, forearm, elbow or whatever that matters, it's how the connection (I believe some people call this a "Communal Lock") to uke is achieved. How the slack is taken out so the limb can be used as a lever to move the body.
We have a really wicked throw that utilizes the elbow a'la a single-armed jujinage. It's just a kotegaeshi at the elbow rather than at the wrist.
That said, the using the wrist generally works better than the forearm for me because there is more lever-arm to provide torque. Like using a long-handled wrench rather than a short-handled one.
Also, the Ki Society folks have renamed their art "Koteoroshi" to better reflect the dropping nature of it versus the turning nature of the kotegaeshi. (This is second-hand, please don't hold me to absolute specifics here).
Best Regards,
Greg Jennings
mailto:gregs_shell_account@yahoo.com
http://www.capitalcityaikido.com/
http://www.takemusu.org/