The coast road speed limit was put in place to deal with a specific problem, people racing over the mountain, then tearing back to Ramsey on the coast road as fast as they could for another go over the mountain, this was causing a large number of incidents and road closures on the coast road, and it does seem to have improved the statistics on that road.

I can't see any changes to the mountain road in the near future though, although an all island speed limit does come up for discussion every couple of years over here but never gets far.