What does happen?
Right now you can only change display brightness (not toggling screen on/off) with brightness keys on keyboard . Also there is no dedicated key to toggle screen on and off with keyboard.
What should happen?
I really like that in MacBooks you can decrease screen brightness, and below lowest brightness, the screen switches off (but device stays on). This is a really nice thing for watching movies on external devices, or let the V download things that take longer (and save battery)…
So maybe it is possible to tell screen controller that screen has one more brightness step than now (which then includes OFF)…?