Qt for Python (PySide/Shiboken)

Poking about the Blender source code, it doesn't look like Blender itself uses Qt to render the UI, so modifying the UI itself would be a bit challenging, however, making your own windows and drawing your own graphics, etc.. That's definitely possible and shown with the blender_pyside2_example repo you posted. I wonder why he has you copy the python3.dll into the shiboken directory — I'd think that would conflict with the python dll of the python installation in Blender.