Ori: "It would be interesting to read a post"

It's only a story (intended to illustrate a completely unrelated point), but do see "That Alien Message."

"that describes how a future society would look like if everyone was given the ability of todays top 2% regarding IQ. What would happen, implications, economic output, happiness and so on."

If you mean shifting the entire bell curve two sigmas to the right, I'll say we can't know in detail because the Singularity would happen soon afterwards. If you mean repealing the central limit theorem and pegging everyone at IQ 131--well, that's a much harder question, because you're changing the mean and eliminating the variance: to the extent that progress depends on rare genius, we could end up worse off in some ways.