Suddenly, you can take a drug that decreases your need for sleep by 50%. People only need 4h of sleep per night now, for a full nights' sleep - 3h, if you're willing to skimp a little, 2h isn't unheard of (in the way that only getting 4h of sleep a night, now, isn't unheard of either).

Suddenly, there's a significant advantage in the hands of everyone willing to take this drug. Students are expected to study more and harder, because they don't need 8h of sleep every night. Entrance exams to schools get more difficult. Software developers are now enticed to work longer hours - longer hours than they already are. Labor / shift workers (hospitality / food industry) are expected to work longer shifts, and they have to, because businesses have to be open longer because more people are awake for more of the day.

Now, also, you have to consider: this is just sleep, in terms of brain repair. Your body has to put itself back together every night, too - repairing microscopic muscle tears, fixing bruises, etc etc etc. Your body would probably start slowly falling apart on 2-3h of sleep per night, even if your mind was fully rested.

I really, really hope this doesn't happen.

Like hell they won't. It will become a social and economic imperative before you know it.

Statistically you are unlikely to be one of those people for whom 5-6 hours sleep daily is sufficient, so all you are doing to yourself is contributing to increased aggression, dulling of empathy and reduced impulse control that comes with insufficient sleep.