So no, bbPress will never be a plugin for WordPress.
(but there will be a plugin for WordPress to automatically INSTALL bbPress, which I think is a different animal entirely than what you are asking)

I assumed it would be a lot more sensible to create a plugin which integrated an existing bbPress install into your WordPress installation. I guess if you can install bbPress with the wp-content/plugins/ folder then that would make a lot of sense though (I'm assuming that's what you have in mind).

I'm guessing getting it to work within an existing WP theme will be quite complex though. Sounds exciting :)