Sensor based vignetting is a real problem for cameras with a large sensor and short flange distance (distance from mount to sensor). This is simply due to the oblique angles of incidence of light hitting the edges of the sensor, which isn't really flat like a piece of film, but contains a stack of objects starting with UV/IR/AA filters, followed by microlenses, colour filters, then many layers of silicon with the photosensitive area at the bottom of a deep well!
Near telecentric lens designs with large exit pupils largely solve the problem, but at the expense of making the lenses larger and more expensive.
Several things can be done to address the problem. Minimising the thickness of the filter stack certainly helps, though Leica attempted this with the M8 but made the IR filter too thin making the camera very sensitive to IR light, causing strange colours in the image (they even had to give out free IR screw on filters to angry customers).
Doing away with the anti-aliasing filter is another option that Leica and Sony (with the A7r) have pursued. Another option is offset microlenses (Leica M9) or elliptical microlenses (Leica M240), both of which attempt to aim the oblique light rays more effectively toward the photosites. The problem with this is that it compromises performance with longer focal length lenses.
The best solution is to get the photosensitive area of the silicon as close to the top as possible. One way is to thin the back of the wafer until it becomes transparent and then flip the sensor around so the readout circuitry is behind the photosite. These so called "back side illuminated" sensors are in existence, but only very recently in anything but very small cell phone cameras.
Finally organic sensors have been touted as the solution to ray angle issues, these have an organic layer that is photosensitive at the very top with circuity underneath. They are a way of production, but promise to eventually deliver the utopia of tiny wide angle lenses that ought to have been the result of doing away with the DSLR mirror!