By the sound of it, it's nothing new. It's called a turbo compound supercharger. They were used on WWII planes. I'm not sure how VW's system will work, but on the planes, the crankshaft would spin the geared supercharger, so it's powered like a supercharger, but it also has exhaust gas runing though it. (Warning, I'm pulling some of these numbers out of my ass.) A normal gas engine is about 7.5% efficient, turning heat into mechanical energy. A supercharged engine is about 10% efficient (depending on the type of supercharger.) A turbo is about 14% (again, depends on type.) Turbo compound is supposed to be around 17%. The only reason it hasn't been used on a car is that it's needlessly complicated, but with the advent of hybrid cars, no one seems to care about needlessly complicated anymore.
One last little thing, a turbocharger is a supercharger...it's just a certain type. Supercharger is basically a category, and there are many different types.
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