Had some time today. This branch has a version of publishFrameTexture which is both OpenGL 3.2 and 2.1 friendly: https://github.com/GameClay/syphon-framework/compare/PSW-OpenGL3 (Diff view)
Here it is all working: http://yfrog.com/z/mgc2wvp
My app is using an OpenGL 3.2 context and my modified version of Syphon publishing using the publishFramebuffer method I added. The Simple Server is using an OpenGL 2.1 context and my modified version of Syphon using the modified publishFrameTexture. The Simple Client is the pre-compiled Syphon example using the current downloadable framework version.
I’m not 100% solid on this, since I’ve only run it on 10.7, but it should run just fine, or require very few changes.