Currently there is no easy way to simulate overcast sky where there is no shadow or just a plane white sky background.
One way to bypass this is to set overcast HDRI and set sun brightness to zero.
Another way to bypass is creating a very large white hemisphere geometry that encompass the entire model.
It would be nice to have an overcast or 'studio' setting, where the environment is evenly lit and the sky is white.
This would be very helpful when rendering conceptual scenes or diagrams where you need a white sky/background and/or no shadows.