Anybody have a clue for what's the packages directory, and how we should use it in our add-ons?
Good question. I'm also interested!
I don't know what your question means, but I know I have had to get into the attach.php file in there to modify my tracker modification. A bunch of the old attachment code is now in there (kinda... it's changed a bit).
It seems all the system will be dispatched into packages as sub-packages (actually: attachments, search, blog, cms, forum).