Looking good! I'm now getting my automatic backups plugin downloaded automatically.
A few thoughts:
This should extend from sublimeplugin.ApplicationCommand, as you don't need a View. This way it'll work when there are no files open, for example.
You may also want to do the downloading in a worker thread.
Also, while eventually there will be options for plugins to display GUI controls and dialogs, in the short term you can use the win32 MessageBox api to display a 'New plugins downloaded, please restart' message box to the user. There's an example of doing it in the ctypes docs: docs.python.org/lib/ctypes-funct ... types.html