I've been making some small progress on Kaffeeklatsch, though most of it is behind the scenes stuff. For example, IEffect now extends IDisposable, and the frontend will dispose effects when removing them. This could be used, for example, in plugins that create OpenGL display lists and want to properly clean up after themselves when destroyed.
At the moment, the core effect library is lacking a dynamic movement plugin, which should deform the color buffer according to a user-supplied formula. I heard that Winamp AVS was made open-source some time ago, so it may be a simple job of porting that effect to C#. However, as this kind of math is not really my area of expertise, I would love for another FOSS developer to join the project and help out there. Post a comment if you're interested.