Sony has a new full-frame camera with just 12 megapixels: the A7s. It seems that 12 megapixels is right out of 2007. So what's the point? Well, the point is high-ISO performance.
DxOMark just tested the A7s and it is the highest scoring camera in the high-ISO category. It beat out the Nikon Df as the "low light champion." If high-ISO capabilities are important, the Sony A7s might be the camera to get.
But there are trade-offs. First, resolutions is resolution. If you intend to make large prints or do much cropping, this is not the camera for you. Also, while the dynamic range is good, it is far from the top in that category (31st, actually).
The price tag of $2,500 seems pretty steep, too. For example, the Nikon D600 can be had for $1,000 less, and it is superior in every category except high-ISO, and even then it is only about a half-stop worse (in other words, it is still excellent at high-ISO).
I'm not really sure why Sony created this camera. Is there really a market for those demanding only the best in high-ISO performance? I can't imagine that there is anything more than a small niche market for the A7s. But Sony has shown that they are willing to take chances, and perhaps this camera will end up proving its worth after all.