the osgearth_tracks sample is showing "dynamic" symbols moving around the earth/map. But the shown aproach has the problem of not integrating well with the layer concept of osgEarth itself. Is it possible to create such a dynamically changing data source with FeatureSource (and call dirty() or something simular) and the FeatureSource rendered output is updated? How does this affect the performance? Is this comparable to the tracks example (think about 1000+ symbols on the map with at least 10Hz update rate with positional changes)?
With the new Layer architecture in osgEarth, you can make a Layer that contains any scene graph. You would subclass the VisibleLayer class and then override the getNode() method to return the scene graph under that layer.
Someday it will be a good idea to refactor the osgearth_tracks example (or perhaps a separate example) and implement it as a Layer to demonstrate the concept.