Except two strokes perhaps.Point taken though.

The only problem is that you need to be able to turn cabin heat off and on
so that would involve high pressure, high reliability valves, two expensive
radiators and high pressure tubing. Perhaps a closed circuit heat exchanger
to a water filled system would work. Now you've added perhaps 3 - 4 kg of
radiator and tubing plus another 4 or 5 litres of water. Hmm, one can see
why the exhaust muff got in there in the first place.

Ian

Not quite so, Ian. The oil cooler would always be cooling the oil,
just what you do with the warm air downstream from it is the issue. A
simple vane valve diverts the warm air either into the cabine or out
into the atmosphere. Simple and light-weight!

Uli