Most of the serious ballet fans on the web seem to be using the Ballet Alert! forums. However, I don't know of any other boards for modern or jazz fans, and this looks like a good place to have one. I would definitely link the Bay Dance site to it. But, as you said, it depends on the numbers.
I still can't see tap fitting in with modern or jazz, or with any other dance for that matter. Tap seems to be in a class by itself.
BTW - How about you tell us about yourself and your plans for Dance Talk?