Interesting logistics there. Are you certain it's as simple as having an aluminum engine block? My old Camry 5SFE had unacceptable heater output in the cold, conversely aluminum engines I've had have spit out plenty of heat ie. small 2.5 V6 gave heat fast and plentiful. You're right that it comes down to R&D and paying attention to proper heat management. Newer engine (thermal) efficiency levels are a newer challenge. With great advances in this area, cabin heating needs to be reconsidered.
For a long time, output-side thermostat designs were used to combat rapid temperature fluctuations, but again poor implementation can negate the benefit of the design like in the 5SFE. When it wasn't freezing cold, the head was busy running too hot.