Question

Is it unreasonable to expect the coefficient of friction to exceed unity

Answer 1

a value of 1 means that the frictional force is equal to the normal force.. A coefficient of friction that is greater then 1 just means that friction is stronger than the normal force.

An object such as silicon rubber, can have a coefficient of friction much greater than unity .
It just means that it takes more force to slide something horizontally than it would to physically pick the object up.