Extracting latent heat from one tank of water and transferring it to another is going to have a cost above and beyond the reduced heating expense in the hot water tank benefitting from the transfer. If you want colder tap water you might get it for “free,” cost of the system notwithstanding, imho.
For relatively low delta T, pumping heat requires relatively little energy. Going pumping from 70 degrees to 110 degrees wouldn’t require a huge amount of energy.
I haven’t done the math but going from 70 to 140 degrees might take twice as much energy. The lower the temperature delta, the closer you come to zero energy cost to pump heat. Now that I am rambling, the math is actually pretty cool as you approach 0 delta the amount of heat pumped per unit of energy expended approaches infinity. Ground source heat pumps are very efficient because they make delta T much smaller, both in the summer and the winter.