I would like to add support for a new "special" request parameter understood by the Sling Post Servlet named :requiredPostProcessors. This parameter may contain a comma-delimited list of names (see below) which must be available at the time the request is processed in order for the request to be handled. Whether or not those processors do anything or whether the request succeeds or not is a separate question; this is just a preflight check if you will.
If any of the required SlingPostProcessors are not available, the request will fail with a 501 error.
The name of a SlingPostProcessor will be defined by a newly defined service registration property postProcessor.name and default to the simple name of the SlingPostProcessor's implementation class if that property is not defined.