I wouldn't go so far to call it junk science. I do believe that monarchies, as far as general trends, tend to have longer time preferences and are less destructive than democracies. But monarchies are certainly not ideal. It doesn't matter what type of government there is if it is not run by ethical people.
It would be impossible for societies to return a monarchical system. We can't go back and recreate what is gone. We are living in an age of individual empowerment and people would never return to a monarchical system.
Since we cannot depend on any political system to consistently produce ethical leaders, the only solution is to come up with an entirely different system, a system that is designed to be the least destructive and oppressive. To me, that would be the private non-monopolistic system that Hoppe brings up at the end of his book. The specifics of such a system, how we can get there, I don't know.
Not even four years hence you both have completely forgotten the lessons of 9/11... and of 2/26.