The TIGERS link I gave earlier implies that there is enough power there to replace ALL of the belt driven ancillaries with electric ones, essentially freeing up 20 hp on the average engine. Electric storage of exhaust gas energy must be doable, and soon; Subaru is ready to replace the turbo on the next WRX with such a setup that transfers the exhaust energy to boost via electricity.
All-New Subaru WRX: What to Expect - Motor Trend