I think making the bboard subsite aware is a definite requirement, but that is orthogonal to the issue of how the message store is implemented and how the email notifications are implemented.
I also like your idea of porting the old ACS3 bboard as a quick
and dirty way to get a tuned and burned-in bboard going. That code is quite ugly, but with some slashing and burning we could probably have something usable pretty quickly. I would only support Q&A style presentation for example. I think I will
try to do something like that, making just the minimal concessions towards cleaning it up, templating it and subsite-awareness, and borrowing some of the basic permissions model from the ACS 4 bboard.
