Much unhappiness is caused by people being uncertain of their place in society or their reason for existance. Think how much existential angst there is in the world, and how much uncertainty there is about the future. if everyone knew what their place in society was and that they were suited for that, then there would be no cause for unhappiness. Under the current climate this is clearly not the case (one only has to look at the goth community to see that society is overflowing with existential angst)
My modest proposal is that if we can advance genetics far enough then for every job we will be able to create a specific human. This will end unhappiness- how can someone be unhappy when they are doing that which is expeditous, wise and best for them, and a job that they were created to do. This would simultaniously reduce human unhappiness because everyone would know their place and their use to society, as proven above, and would increase human efficiency due to everyone being designed and optimised for their specific job. For the few unfortunate souls that are still unhappy, obviously you can't get the engineering perfect first time, and these mistakes can be repaired.
Furthermore, you could optimise humans for specific functions that are currently impossible for humans to perform unaided. You could make many people green skinned due to chlorophyl, meaning that they didn't need food and could survive very well in sunny environments. For space you could go for a black rubbery skin, very light bones and a massive lung capacity with the goal of having people capable of surviving in space without a space suit. You could even go further here and say that in space, two arms good, four arms better. For swimmers you go for a blue skin, gills (probably over the rib cage for more direct access to the lungs), webbed hands and feet. For politicians you want a gleaming silver so they can be seen, a teflon coating and a transmitter to warn you of their approach. You can do a simmilar process for almost every job conceivable.
I have a dream that one day a man can be judged not on the content of his character but on the colour of his skin.
Women, of course, will be completely incomprehensible whatever happens.