Formula 1 already does this. From what I can tell, it requires a really long shaft between the compressor and the expander sections of the turbo, for thermal re

Formula 1 already does this. From what I can tell, it requires a really long shaft between the compressor and the expander sections of the turbo, for thermal reasons, so it's a very expensive piece of kit. Also, it requires that your typical driving scenario frequently dumps a lot of flow out the wastegate, which is known as "driving like an idiot" on normal roads.