There isn’t any official documentation as far as I’m aware, but you can read the IRC logs on the blog (https://bbpress.org/blog/).
Regarding the points by froyo:
1 + 2: As mentioned it would work in the same style as buddypress which allows plugins which affect particular aspects of buddypress itself. So there wouldn’t be a problem hooking into only bbP features, and keeping other plugins away from bbP.
3: I think the admin area will be a whole lot cleaner when the two are integrated. Currently all the user stuff is duplicated in both admin areas (and behave differently), so I imagine there will be additional menu on the left of the WP admin area for all forum related stuff, plus a dashboard overview panel/widget.
