Handling attachments - there is a basic profile for specifying attachments but of course nothing obeys this. So, we potentially need user guidance in the form of configuration ui for these various options including the ability to override all the clever processing and just have a 'give me the request body and return the response body element' style invocation as a fallback.
Proper file extension for workflows, for instance .scufl. Make it easy to double click, and avoids confusion with saved output data. Could also suggest a mime-type.
Make a proper double-clickable launcher for Windows, like on OS X