The current display technology of mobile phones consumes a lot of power. As a consequence future display technology will propably support more than the basic ON and OFF modes. Current smartwatches like the Sony Mobile SWR50 SmartWatch 3 already supports such a new display mode which Android can use in the so called “Ambient Mode”. This is some kind of passive mode which can save a lot of energy while displaying information in a low-power state of the display.
Ther are already some examples around the web showing good use cases for such “Always-Alive” apps making use of the so called “ambient mode”. I think that the Wake Lock API should take the low-power display mode of future display technologies into consideration.