My "flying car" is world peace. In the mid to late 80s (this would be from when I was 10 - 14 or so), I was convinced that by the year 2000, we would have a peaceful planet, either because some of the cultural trends I was seeing (80s TV was deceptively optimistic in some ways) would win out, or because we would finally nuke our civilization away. And I was looking forward to either one, because if I survived the nukes I had (naive) plans for how I would survive and even prosper in the post-apocalyptic world that mainly revolved around having taught myself how to build electrical generators and motors from natural materials.
But just like flying cars, we don't have world peace, and I now believe I understand that we never fully should unless we meet extraterrestrial civilizations to unite in our dealings with. Just us, humanity, we should never have fewer than five nations, and probably always more than that - consolidate too much power in one place and there goes freedom.