They did something very similar 20+ years ago called XL1 to achieve 1l/100km, never made it into production. https://de.wikipedia.org/wiki/VW_XL1

Seemed to have been produced a bunch for never making it into production

> A limited production of 250 began by mid 2013 with pricing started at €111,000 (~ £119,000). As a plug-in diesel-electric hybrid, the XL1 was available only in Europe and its 5.5 kWh lithium-ion battery delivered an all-electric range of 50 km (31 mi),[3] had a fuel economy of 0.9 L/100 km (310 mpg‑imp) under the NEDC cycle and produced emissions of 21 g/km of CO2.[8] It was released to retail customers in Germany in June 2014.[3]