I seem to remember that VW(?) tried a heat storage system, possibly using a small vacuum-insulated tank in the engine bay, to store hot coolant from when the engine was last used, and to provide a rapid warm up, using some sort of heat exchange system. I imagine the additional weight and compexity of such a system would not be insignificant. I have noticed how much longer, under similar temperature conditions, it takes my CRV to produce any useful warmth compared to a friends Matrix which provides warmth very soon after start-up.