The policy is a good start, but short-sighted in its materials specification. Clay has been used in sewer systems for centuries. Plastic pipe has been in wide-spread use in sewers for less than 70-years. How long do you think it will be before plastic pipe starts to suffer its own issues? It's already happened in some systems. If you're going to legislate inspections and materials for replacement, it should really include all sewer pipe. Not just the oldest materials (clay & ductile iron) in your system.
The policy is a step in the right direction, but very limited in its scope. How long do you think it will be before some of the newer plastic pipe starts having issues? In many systems it already has.
So a policy that is limited to only certain kinds of pipe material is incomplete at best.
Most systems over 70-years old were designed to allow a certain level of dilution. Now that dilution is an expensive and environmentally unfriendly problem -- don't blame the pipe materials for the state of the art when they were installed.