LOL there was a company here in the Netherlands that even put a Smart turbodiesel in an offroad motorbike. I believe they shipped the majority to the US and Canada before going bust.
But still, to me it would be a shame to convert such a nice EV to some fuelburner, whatever the type. IMHO it would still be nicest if the batterypack could be used to house batteries and a BMS again. If the rest of the car is still good to go, of course. Those batteries look like you could fit standard batteries in as well...
PS for Cobb:
2002 Audi Audi A2 1.2 TDI "3L" Gas Mileage (A2 3L) - EcoModder.com
No boattails or any big mod, best tank 104 mpg
Think about it: why do those big rigs run on diesel?