With the advent of the record/serialization framework and processors, it would be nice to have implementations where the user could script the reader/writer using the same scripting capabilities that are in the scripting NAR (enabling ExecuteScript, InvokeScriptedProcessor, and ScriptedReportingTask). This would allow for prototyping of record readers/writers for which there are not yet full implementations in NiFi (XML, e.g.)
These scripted record handlers would not (easily) be able to leverage the SchemaRegistry for schema management; although the SchemaRegistry interface is in an API JAR, there are many utilities, base classes, etc. that are in the services NAR. Instead the scripted reader/writer would be responsible for determining the schema, perhaps by letting the user set dynamic properties, e.g.