I am not sure if such a converter would handle a Twine based web-application (nor any web-app for that matter) due to the fact that the code of each of the Story Format engines assumes that there will be a HTML render and Document Object Model for them to interact with.
Each of the current Story Formats are a mini web-apps, the Twine application embeds the different types of Passage data within this web-app, and the web-app is responsible of converting the contents of a Passage into HTML / CSS / Javascript as and when needed. The engine is also responsible of defining the macro language and implementing all functionality required to support that macro language as well as any of the features that engine has.
What you could do is create a new Story Format template/engine that was based on a Java-application instead of a web-app, such an engine would need to be able to convert the contents of a Passage into whatever code is required by the Java-app, it would also need to implement all required functionality like the macro language.