My vote for the most under-rated technology, the sleeper that's most likely to completely alter the future in 50 years or so, is virtual reality. VR isn't very visible in the consumer market right now. I guess the novelty wore off after it was introduced 15 years ago in video arcades.
The headsets were clunky and the graphics were pretty poor. Back then I thought game companies would go after VR, and they did for a short time, but interest wained.
I like the films about VR: "Lawnmower Man," "Dreamscape," "Vituosity," and "The Matrix." In a way I like Lawnmower man the best, even though it was objectively the worst of the films I mentioned. The other films posited that we'd want virtual reality to mimic real life. Only Lawnmower Man posited that we might prefer to live in artificial, man-made worlds which resemble abstract video games like Mario Brothers.
One day, maybe in our kids' lifetime, quantum computers will give us the power to create whatever worlds we like. Almost certainly a lot of people will prefer VR to the real world. Some might not even feel like eating and may starve to death. If I could fly, if I could reach for things with arms as long as football fields, if I could be an insect or a T-Rex, if I could sleep in a bird's nest or be a fish in a lagoon, if I could have unlimited sex and explore the atomic world by flying through molecules....if I could do all that, maybe I wouldn't want to leave the virtual world either.
On the other hand, maybe reality is the ultimate virtual world. There are so many weird and unpredictable mysteries, even in a leaf. Maybe the more realistic VR gets, the more people will learn to crave and appreciate reality. Who knows?