I was experimenting with live compositing workflows with Solaris and COPs, and curious to know if it is, or should be, possible to get the output from a USD Render ROP into a COP network using the render COP.
I don't think so, the Render COP requires a SOHO-style ROP. It'd have to modified to support other ROP types. All it does is to redirect the filename (the Render COP is really just a button-presser followed by a file load).