If a person were to give it a serious try, I would limit it to a single glazed vertical collector with some form of overhang above the collector to protect it from summer overheating.  Protecting the CPVC pipe from UV exposure would probably also be a good idea.  

I've thought about using PEX, which is somewhat "tougher" all around than CPVC, and the tube wall conductance is better.  For vertical space heating collectors, a serpentine tube PEX collector that uses the formed aluminum fins with the fins placed between the sun and the PEX, and something like single glazed SunTuf (which cuts out UV) might hold up for a good long time.  It would not be as efficient as commercial copper/copper collectors, but it would be so cheap you could make a lot of it.  PEX-AL-PEX has better burst pressure, and once you push it into a bend it stays holds that position -- this should make it easy to do a serpentine collector with no joints.  Somebody should try this :)