I hope f.lux becomes irrelevant once dark mode becomes the standard in all devices. If the web catches on and if our screens become OLED (or use any technology where dark pixels aren't illuminated), then "night mode" will be seen as a crazy hack.
"Night mode" is still useful with Dark Mode. In most applications Dark Mode still uses plenty blues and greens for accent colors and often strong whites for text colors. Even if fewer overall pixels are dedicated to those colors, it's still useful to color shift them away from blue in the evenings.
How do you like viewing maps in dark mode? I tried Apple's Maps app on macOS, and it felt weird -- like navigating at night. Otherwise, dark mode seems good.