Mike, general centrifugal impeller such as used in turbocharger and some superchargers are rev up to much higher rpm than the engine operates at. Ernest concept involved using the engine rpm (direct drive so to speak) which is much lower than the rpm these centrifugal impellers require (for any useful pressure increase).  So slower rpm generally means larger impellers than commonly found in turbo or superchargers.  If not constrained to the engine rpm then yes, your suggestion would have merit - on the other hand,  there may be impeller off superchargers of those big multirow radial engines of WWII that would be large enough - probably hard to find and heavy.