Modern vehicles have variable intake runner length, that gives at least two rpm where intake is tuned for, but I guess it has not been made for exhaust yet?
It would require quite bit of work to get such system made so that it would work for few hundred of thousand miles, but that would offer again bit more efficiency when there is less compromise needed
But exhaust manifold on many cars is quite horrible, all exhaust ports can have different length of manifold pipe attached to it, while those pipes should be equal length, at some cars exhaust manifold is log where exhaust ports are at one side and gases exit from one end of log, quite horrible.
Replacing exhaust manifold and adjusting motor to change should give a nice improvement, especially when both intake and exhaust manifolds will be tuned for low rpm which is used mostly when driving.