bbPress can already be synced with WPMU. What sort of MU features are you looking for?
Sam mentioned a year or so ago that:
There will be a sort of super plugin that you will be able to integrate into bbPress to get most of the functionality of TalkPress. The working name for the project is “bbPress Channels”. It will be released after TalkPress.
TalkPress is their hosted “bbPress MU” – so it sounds like eventually, we’ll have the ability to host multiple bbPress sites from a single install.
They will be releasing the code soon but not yet.
Do we have an updated status on bbPress Channels yet?
Since Sam stepped down as bbPress lead a short while ago, we haven’t heard who will be replacing him (or how many resources Automattic will devote to the product). Hopefully we’ll get an update sooner rather than later!
I am praying you are right. This feature is extremely important!