I need to have access to the angular/linear velocities used to calculate relative velocity. This would allow them to have a simple working solution for their collision behavior.
Without the velocity types used to calculate .relativeVelocity, the value is not useful as you do not have context of what the two velocities were at collision time.

(Rather than using the workaround - ContactModification in order to retrieve linearVelocity, angularVelocity at collision time)