I detect the law of unforeseen consequences kicking in here.
It will depend on how large a particular pay area is. I could see some people drifting towards the higher paid jobs to the detriment of the poorer areas.
Even if uniformed personnel are exempt, what of their wives? A wife with a secure CS/NHS job paid X will not want to swap to an area paying X- with the knock on effect to her pension rights.
A nurse already gets hit as they often start a new job at base rate.
However I see the initial plan is only for a few lower paid in DVLA and Job Centres. Will the minimum wage also become regionalised?