I used f.lux on my PC for a year or two but ultimately removed it because it occasionally caused the screen to flash (can't recall but probably on sleep / wake-up / UAC actions). Sometimes it would stop working altogether. If I were Apple, I'd be skeptical before allowing a low level driver access to an app that can potentially affect the device experience. I'd want to test it to death & be damn sure that the benefits outweigh the cost of allowing it.

On a related note, the linked BBC article talks about phones needing a "bed mode" to "protect sleep". If you are really struggling with eye strain / disturbed sleep, a better advice would be to turn away your gadgets well before bed time and avoid the compulsive behavior of reading on your phone all the time. I tried f.lux along with better ambient lighting, screen dimming etc. (suggestions found on HN). The benefits were marginal. I would still wake up with groggy eyes & felt sluggish until I experimented with the rule of "no gadgets after dinner". That helped way more.

Don't get me wrong, it may be an awesome piece of software for those who have to be in front of the screen for longer duration.