Initially your idea sounded on point, COOOOOOLLLLL. I imagined it being a plugin to Stardock Central as a separate "Launch IM" option. It could work similar to IRC in that you would see a list of users who are logged into SC and privately IM one of them or start a chatroom and invite people to it...
However, after further consideration, I believe that WC has skinners covered between IRC and the messageboard (incl the suggestion for the "new" board). If a skinner would like feedback on a particular idea of his/hers, then chatting privately on IRC, providing his/her AIM, Y!, MSN or ICQ SN, or even posting to the messageboard or channel would be an option.
For those who do not wish to use IRC, again the messageboard is a venue (available to everyone with a web browser) to initiate a thread wherein feedback can be requested.
Moreover, if one would wish to start an AIM chatroom or the like he/she could do so. I think paxx has got it when he says that programming would have to be done and I would imagine there really isn't development time available for such a venture.
