The assumption is that the sensor is exactly the same size, and that the pixels are smaller. That may be so, but we don't know any of that for sure.Marc
The 50MP sensor can not be much bigger than the 39MP sensor , due to the H-SYSTEM body design .
If the sensor has the same size than the existing 39MP sensor it might also produce more noise and moiree at high ISO .
PHOCUS might take care of this issue.
It may be a true FF sensor ... or if still a 1.1X sensor size, the pixels may be larger than we think due to advancements in reducing the space between pixels.