The obvious thing to do would be to make the Action subclasses have public names.  I personally would continue to use the strings, though, as they are easier to type.  (The same would be true if an enum were introduced (that I'd continue to use the stings because they are easier to type :), since they would need to be namespaced (argparse.action.store_true, for example).)

I can see some potential value in exposing the action subclasses, but I'm not sure if it is worth it.