There was an event today where Mexican President Enrique Peņa and Sir Norman Foster presented the project for the new MEX.
According to the announcement, the project will be built about 8 miles to the northeast of the current MEX. The first phase will have 3 runways with the possibility of simultaneous operation, 95 gates and 42 remote stands, capacity of 50 million passengers/year and 550k operations/year. It would be possible to expand it later to 6 runways, 120 million passengers/year and 1 million operations/year.
There's a video here:
https://www.youtube.com/watch?v=jwsJnNd__1I
The official website for the airport project is at
http://www.aeropuerto.gob.mx (the video linked above can be watched here as well).