you are correct C3D is deficient in that one can NOT specified max grade change to trigger automatic vertical curve and or warning flag.
Thanks for the confirmation, MJF - somehow 'incomplete' just doesn't seem to be sufficient, given the topic.
Methinks this should be as simple as Autodesk adding a new 'PVI Grade In', and 'PVI Grade Out' Expression (or a [this] Tangent Grade, Next/Previous Tangent Grade, etc.)... For notifications, that is... Obviously, auto-Vertical Curves given a violation would be an ideal end-result.
Cheers