That won't really solve anything. Determined users can up the gamma/brightness on their monitors, in their video card control panel, or using a third-party app like Powerstrip. Now, opinions may sway when the moon phase changes, or as more people learn to put HDR to the highest setting (try it!). Right now, there's a huge influx of new users who may have only seen this game as a 'stumbling through a dark forest bad peyote trip' simulator. And, given the popularity of this thread, the near-unplayability of night is an issue. However, this is meant to be a survival game, so a balance needs to be struck. Vision in the dark should be just enough to avoid walking into huge trees, kind of like the background for the site here. Zombies are best when they "emerge" from the darkness, giving that sense of panic, and the everlasting fight or flight choice...do you shoot this zombie who's just startled you (and risk five more coming at you from that same darkness) or attempt to slip away? I think extending the power of the HDR visuals would be a great way to keep the brutality and challenge. By actually going for realism and mimicking the eye's slow adjustment to darkness, you leave two more interesting options. You could sneak around in the dark, keeping your eyes accustomed to deep shadow, knowing that the muzzle flash from your stealthy gunshot will burn an afterimage into your vision and plunge into blackness anything more than moderately dark; alternatively, you could throw a flare (or flares) to define a combat arena, where the flash is an inconvenience at worst, and you can see the zombies more clearly, but only in a small area and one that's visible from klicks off, attracting more nearby zombies and possibly faraway bandits.
