runway2,
a person by name of overun said that in differential friction was also and operation issue
john-tullamarine has gone to the heart of the answer in terms of separating the operating-piloting issues, and the airport engineering issues
. . the engineering/Standards desire to have reasonably uniform frictional characteristics across the runway .. consider the analogous situation in your motor vehicle on a very wet road at speed .. each time you put one side of the wheel geometry into a puddle, the car suffers a quite noticeable yawing/steering torque to that side.
Yaw angle and the like are operating-aircraft issues. Differential friction is predominately an airport engineering issue.
I have wondered from the start of this topic whether the question was some sort of indirect airport engineering question which is testing the acceptability of a runway deficiency – maybe a rutting/ponding problem which already exists or maybe someone is thinking of grooving the runway only 30m wide on a 45m wide runway or maybe the runway is widened (or is going to be widened say to 60m for the A380) and the surface of the widening is different to the surface of the existing runway?
Well the answer to that is short and simple. Deficiencies in rutting/ponding or friction are not acceptable.
The earlier PPRUNE discussion that you referred to was about minimum runway width, and the conclusions reached related to Vmcg and engine failure on takeoff. That discussion should not be extrapolated and applied to the issue of differential friction. Differential friction as a specific airport engineering issue would have to be addressed using other means. This is a very specialised area and only a few names like AEA or NLR come to mind as being able to do this.