IOTL Emperor Joseph II had only two daughters. Thus his title of ruler of the Habsburg realms (and thus the Imperial title) went to his brother Leopold II, who had sons (and was thus succeeded by his son Emperor Francis II/Francis I of Austria).
So what if Joseph II has at least one son? Obviously, said son would become head of the Habsburg family and likely Emperor as well. Would this help in ensuring Joseph's reforms largely stay? Would the Habsburg Monarchy be able to avoid its stagnation in the 19th century?