I am wondering if you are considering to use html5 widgets if available and provide a fallback gwt implementation for browsers that do not (yet) support widgets like http://slides.html5rocks.com/#semantic-tags-2
I think in general GWT has the right tools for using native browser stuff whenever available and providing some js-pendants if they are not supported. -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
