As I mentioned above, CesiumViewerWidget has become a dumping ground and a lot of the code is ultimately going away in favor of new widgets.  CesiumViewerWidget was never meant to have applications built on top of it.  That being said, updateAndRender exposes the default render loop function so that you can easily use multiple widgets on one page.  All of these things will continue to change, some of them before the next release, so we can't possibly come up with the best solution in the animation branch, we will work on it  in the cesium-widget branch once this is all in master.