Re: what about bp-plugins?
It’s a good idea and one I’ve tossed around, but the problem is that it would need to exist outside of the wp-content/buddypress/ directory to avoid automatic update problems, and people wiping out the plugins folder on accident (if they do a manual upgrade for example.)
Something like this may still happen down the road, as BuddyPress grows and a need for specific methods to register plugins with BuddyPress increases. At the moment it isn’t necessary because BuddyPress plugins are actually just normal WordPress plugins that may take advantage of BuddyPress features and API’s. (At least, that’s how plugin authors should be writing them.)
What will need to happen for sure is a way for plugins to tell BuddyPress “hey I’m here and I want you to know this information.” It’s possible to alter the $bp global directly to do these things, but tighter integration into the platform makes sense.
My opinions are subject to change on this one, but today that’s how I’m feeling. 
