I started working on this.  A couple of things I'd like a little feedback on since I'm a sourceforge newbie.  First, I was thinking I'd develop the add-in as in independent solution with its own build file. I was not going to check in anything until I get a marginally stable application.  I was then planning on adding a module called /cvsroot/sharpcvslib/sharpcvslib/addin in the existing solution. All my files will be in addin. 
The other thing I was thinking about doing is localizing the application so that it'll be easy to support other languages. 
John A. Murphy
Home Page http://www.murphybytes.com