Sony has been on a roll, pushing envelopes in not only sensors (e.g. the 36MP CMOS sensor found in the Nikon D800), but in bodies and systems. The recently released Cyber-shot DSC-RX1 and RX1R variants are closer to what many people expected from Leica in their Leica X2. (The new Alpha 7 series might be what those same people expected when Leica teased a "Mini-M", and gave us the Leica X Vario instead.)
The Alpha 7 and Alpha 7R are about the same physical size as a large Micro Four Thirds camera, like the Olympus flagship OM-D E-M1; but with a sensor twice as big. The Sony A7 and A7R fit a full-frame 35mm sized CMOS sensor into a small body, with either (for the A7R) a 36MP sensor and no low-pass filter (like the D800E) or (for the A7) a 24MP sensor with on-sensor phase detect auto-focus sensors. That's a bit of of an odd choice, either high resolution *or* low resolution but faster focus tracking, for a body that is small enough to carry out of the studio. Comparisons against the D800E from the higher resolution model A7R have been positive, although the A7R tends to soften to more modest resolution towards the outside of the frame.
The A7 family will use Sony's new FE-mount lenses, as well as support existing E-mount lenses with an APS-C sized crop. Initially, users will be able to fill-in their lenses from Alpha-mount lenses using an adapter.