While it goes along with a central knowledge base, this suggestion might belong in it's own thread.
I would like the ability to share documents from my "company / document" or a central knowledge base repository with a client through their portal, not just as an emailed link. This way, I update my "master document" and it is reflected across all companies it is shared with.
Bonus points to include on the fly variables like company name. Example:
Document prepared for %CompanyName%
Would expands to when viewed:
Document prepared for @johnny