With the actual announcement of the camera's release, there's no reason to speculate any longer. At least not any more than one has to when translating brochure-speak into tech-speak.

Essentially, on the new Canon sensor, each pixel consists of two photodiodes side-by-side under a single microlens. During the picture-taking operation, the two photodiodes act in concert (their outputs are summed/binned) to produce a standard single-pixel output. During the focus operation, on the other hand, they are read independently, so each photodiode is receiving light from a different angle through the microlens. Because the angle becomes significant, the imaging sensor can act as a phase-detection autofocus sensor.

That's the mechanics (or optics) of it, but that still leaves some questions that can only be addressed in testing and reviews. For instance, since imaging pixels are being used and imaging pixels are very small and only half of each pixel is devoted to one of two angles of incidence, how will that affect low-light performance? Are adjacent pixels ganged in a different way to provide greater sensitivity? Do the splits occur in only one direction, or in multiple different directions across the sensor. (This is essentially asking "are all of the focus points vertical, horizontal or cross-type?") Is PDAF available across the entire sensor or only in defined focus point areas?