Temperature can be measured in different ways. IR radiation and sound can be measured from a distance. The relationship between temperature at the source, of the water exiting the showerhead and time can be learned. Water can be heated in different ways. The valve could also be a pump. Our reaction to the temperature of the water can be sensed.

Who knows, AI can come up with simpler or cheaper solutions that did not cross our mind. I would say, time will tell.