While I think that an "International coordination list" would be helpful, my assumption is that ICANN's idn-discuss list (see http://www.icann.org/topics/idn.html for subscription information and some other information that might be useful) is intended to serve that purpose.
It is pretty clearly not this, or any other, IETF list: the IETF made a series of fairly explicit decisions to not get into the business of deciding what things could or could not be registered within the very broad coding mechanisms specified as part of IDNA.