Not entirely true ; for example, the D1R supercharger has been CARB certified, and Bob produced only 62 units . But yes it’s an expensive process and since catalytic converters don’t fail very frequently there may not be an appealing market prospect in building those, for what may be an extremely limited demand.
And as for CARB not allowing even testing of cars if aftermarket parts which could affect emissions are detected on them , I refer again to the above noted SC set up …All that smog testing stations need to see is the carb sticker number, and once that’s registered in the Ca DMV database with your car’s VIN, there is no need to do anything else for any of the flowing tests .
I recall reading here that a handful of people were questioned by smog testing places about cat-back systems on their 968, and had to explain to the testers it had no effect on emissions, but none received any push back or refusal to have the test performed after conveying that. ( I was never asked anything about my BB cat-back at any of the tests ( that was several years before the SC install ) , but once the SC went in, at the first emissions testing the technician was scratching his head at the sight of it, unsure where to go ahead with the test of not …until I pointed him to the CARB sticker inside the hood. All went seamlessly after that ..
And on a separate but related note, a friend of mine ( who is a very apt mechanic ) with two 968s is converting one of them to a full electric car . It’ll be interesting to see how that goes ..he said he’s by no stretch the first to do that , there’s much precedent for those conversions ..but it may be the first “ 968 E “
:lol: 
