If Canon or Nikon wanted to produce a stupidly high (100MP+) megapixel full frame 35mm sensor they could. The pixel density on their compact cameras is about .3

If Canon or Nikon wanted to produce a stupidly high (100MP+) megapixel full frame 35mm sensor they could. The pixel density on their compact cameras is about .3MP/square mm, a full frame 35mm sensor is 36x24mm (864 square mm), yielding a ~260MP sensor. They keep their high end bodies at a much lower resolution to increase the available dynamic range and enable shooting in much lower lighting conditions. It'll be interesting to see what they pulled off, but in low light situations (or high contrast) is where you'll see the issues of cranking up pixel density start to crop up.