Right now, Magnolia will include/exclude items from being cached based on various rules.
One can even influence cache behaviour by setting cache headers in the response before rendering starts (and response is committed).
However there is no way to react based on some arbitrary events that happen during rendering or based on the response code. This would for example allow excluding items from cache in case someone generates number of 404 requests just by trying to fish for valid URLs on the site.

Attached is an example of executor that would not store items in case of errors, but rather then having specialized executor, this behaviour should be configurable.