CSS 3 has a working draft concerning extended supports for fonts: http://www.w3.org/TR/css3-fonts/
This draft include the support of fonts loaded dynamically by webpages: http://www.w3.org/TR/css3-fonts/#font-resources
Currently, WebKit implements this feature by loading the fonts with QFontDatabase::addApplicationFontFromData(). This causes a number of problems and does not follow the scope of the specification (e.g.: https://bugs.webkit.org/show_bug.cgi?id=29433 ).
Following the specification, the fonts loaded by a webpage should be only available in the scope of the webpage, not in the scope of the entire application: "Downloaded fonts are only available to documents that reference them, they should not be made available to other applications or other documents."
To implement this feature in QtWebKit, new APIs will be needed in Qt.