QWebEngine lacks method to handle unsupported content

I'm finding that QWebEngine is very limited in it's ability to deal with
various files. In Qt webkit widgets, I was able to handle most file special content with QWebPage's unsupportedContent SIGNAL. In my case I was able to listen for the signal when a ODF file was loaded. Then using a user-script I could redirect the page to a javascript based ODF viewer and it would render the ODF inside of the view.

Is the content unsupported hook never coming back? Is there a way to at least get the mime type and do something similar with the QWebengineDownloadItem?