as quartz renderers are openGL there might be a chance to attach a screen capture type of that window, hoping that render window will keep pushing frames when it does not have focus.. This type of solution should work for grabbing any render window on mac or pc (yes I am a PC VVVV guy..).
It might be better to develop two separate yet similar solutions for mac and PC. The mac side should be able to integrate QC somewhat easily and load patches like video clips similar to vdmx (that functionality is the coolest, I admit). As for PC side, something that uses buffer grabbing functions like fraps or bigFug's winampStreamingPlugin (the mem option is hella fast..), this would enable sending vvvv or processing into resolume as layer (or allow us to use both old freeframe and ffGL's so that I can use bigfug to stream vvvv into resolume3).
Eitherway great idea, tighter integration with other render windows is key. Flash isn't the only generative content creator.
Asus build - intel 2.8GHz T9600, 4GB 800Mhz DDR2, ATI 4670
Rack unit - intel 2.7GHz q6600, 8GB 1066Mhz DDR2, 9800GTX+, intensity HDMI input card