There is already a plugin interface which would allow you to create your own java program and distribute a .jar file along with jemplode. It's documented here. I guess I would rather see Mike work on some other requests other than a scripting interface first (especially a comprehensive website with all relevant links, documentation, betas, etc.). The plugin interface would suffice in place of a scripting interface for now anyway.

But I agree about custom code/scripts for JEmplode, it would make things a lot more flexible.