Can it show addresses to autocomplete even if you don't have created contacts for them?
That's what I want to achieve, and what is currently possible with mu (and notmuch, but through an ugly hack).
I like treating contacts like favorites. I don't manage any, and let my email client / web browser handle them based on frequency.
No, BBDB doesn't maintain separate lists of "real contacts" and "seen addresses". On the other hand, contact creation is cheap, and can be totally automated to happen behind the scenes, without your involvement, so the effect can be similar.
As far as I know there's no integration with notmuch, though. That's not too much of a problem, however, since the only thing you're missing there is the ability to create new contacts automatically from received messages. But you're almost certainly reading new messages in Gnus (where BBDB contact creation works), not in Notmuch.