Personally I think it's awesome that it can get that dark.
I think they should leave it that way and maybe add occasional ambient lighting, like some times stars and moons will produce enough like to just barely see, other times it will be blackness like in the video.
I think that makes it kinda hardcore. They could even make monsters that can see you in the dark but you can't see them. Kinda like that one movie. I think that would be a great experience, and a reason to add more items to the game like flashlights and night vision or thermal optics.
Night-time at Calypso should be more terrifying than daytime. We intend to release creatures that only operates at certain times during the day/night cycle, with nocturnal-only creatures.
And, of course, new tools to help out, like NV goggles, MF, lightsticks, etc.