I couldn't see one infringement by a 'low & slow' rag & tube type (Cub, Luscombe, Tiger Moth, Aeronca ...).
Given those types are likely to be returning a weak and fading primary return only (no transponder) they can't be easily tracked and identified.
Also without Mode C one cannot tell one has a vertical bust, in any airspace that doesn't extend to ground. Even if the bust is a bust (say in a CTR) one cannot estimate its seriousness relative to other traffic (no height info) so I would bet that reporting action is less likely to start with.