The brightness hotkeys have no effect in Ubuntu 16.04. My laptop is an ASUS G752VL-DH71. I'm running proprietary graphics card drivers (after enabling, I could at least toggle brightness manually.) The graphics card is an nvidia geforce gtx 965m.
I tried the update suggested here without any success.
Some other hotkeys (volume) work.
Edit: now the brightness control doesn't work through system settings either, regardless of gfx driver.