The most tantalizing part of Matt's statements above for me would definitely be

...and profile features, in particular, are useful to the future of discussion forums

Any mention of profile features makes me giddy. I've just come off a large project and the one thing lacking on my install is extended profile fields. Over the past year, I've investigated and tested several different plugins that attempt to let the admin create and manage custom profile fields, and then tried to integrate those into the registration form. None of them panned out. I am hoping that if the bbPress plugin sees the light of day, then it will include (or lead to) an easier path to creating custom profile fields and integrating them with the registration process.