Well.. that's a nice start.
Here is what and how - I think I mentioned earlier - using micronormal maps would work, which is by FAR much faster that processing it in code or nodes into the Environment and specular aspects of the shader. It has NO hit on performance, or none that I know of.
So, using my shader that Stan and I developed for the passes, and with the default secondary normal map I have placed, you can tile it to quite high values. So using the Diffuse value, I inversely influenced the reflectance, and made the normal map stronger and more tiled inversely. So more reflectence, the more tiled (smaller) the micronormalmap would be, also less/more height values accordingly to not distort the environment map too much. Obviously I'd need to finetune the settings and make a single controller that would drive all those values dynamically - but you can achieve that system without much processing... well other than the dynamic aspect of the shader driving those values.
Ultimately I consider roughness to be.. molecular roughness, microscopic.. so why not use the beauty of normal maps on microscopic detail to achive the "blur" roughiness?? No or little visual performance hit. Though, the little normal map can only get so large tiled that you begin to see it's rough detail as not so "microscopic" but noisy..
Ultimately, PBR usually doesn't have a Specular driver, so that would have to be dynamically configured too, to dynamically change it's value with the reflectance/diffuse and Micronormal map values. When.. I have a bit of time and want to do something large or interesting in trueSpace again - I'll develop that. I miss having realtime AO. I will need to work on my false AO lighting rig a bit more.....
