That's a variant on a very old idea (the original Victorian plumbing in my house made much use of hot water loops) but I'm not at all convinced that it would improve efficiency. It's also worth pointing out that modern washing machines and dishwashers (at least in UK) use such ridiculously small 'puddles' of water to do the washing (and often very low temperatures) that I doubt that, efficiency/cost-wise', it makes a lot of difference how the water gets heated!Intelligent designers specify a hot water loop circuit back to the hot water cylinder, with a pump connected to a motion sensor in the kitchen, with all pipes insulated.Turn on the machine and cold water from the pipe flows in followed by water from the tank / boiler.
Kind Regards, John