Why not just use the IRC?
More technical people probably will continue to use IRC. That said, many others won't, simply due to the barriers to entry. Our take, is that topic-based discussions are of interest to a lot of less-technical folks, too. For them, something like Chapp is easier.
Edit: in fact, Chapp itself could be built on top of IRC and retain all of its current functionality. You'll also gain a very well battle tested protocol and software tools.