skylight portal with property for scattering light

[Dschaga]

coming from lightscape i know that there is a difference in rendering between an opening(no glas) and a window (with glas).
The light is scattered when using a window.. it's a more diffuse lighting.

The skylight portal is nice but not if you want to simulate the effect of scattered light through glas.

What about a slider which affects the scattering from no scattering to a scattering of matt glass?
We could then simulate glas with the vraylight and exclude the real 3d model of the window from generating GI...