Since Qt 5, QWindowsMime has been removed from the publicly accessible API (unless I am missing something). Because of this change, it does not appear that it's possible for an application to implement handing of additional MIME types that could be done in Qt 4 using QWindowsMime.

I should note that the Macintosh equivalent, QMacPasteboardMime, does exist in Qt 5.

It looks like the class still exists internally in Qt5, but I don't see how I can access it from my application.

See also QTBUG-39558.