I can load a layer, open a canvas, and draw the layer in the canvas using the Qgis python API.
Can I bring up the properties dialog, or even just the "Style" tab of the properties dialog, from such a standalone application? I have a bad feeling I can't because all the code is in the main Qgis Application rather than present in qgis.core and qgis.gui, and doesn't have a python interface.
Unless I've missed something, the solution might be to rebuild the dialog and its behaviour in Python, re-using the relevant .ui file?
guibut labels are not yet.