From a comparative political science view, I see merit in a const'l monarchy. I don't see how Britain is less free than America by a constrained monarch. Americans could use someone beyond the fray. Americans have an addiction to the royal family. My concern would be the cost of maintaining the monarchy. She only pays very little tax and receives countless millions.
I also like the parliamentary vs. congressional scheme in many ways. The party in power can truly lead. America is almost in paralysis now b/c of party politics. There are down sides, of course.
It is pretty well established that the Duke of Windsor was a Nazi sympathize. I expect very shocking news to emerge with time. Hitler had in mind to succeed or reclaim the throne when England was invaded. One person cannot undo the concrete actions of many royals.
I do quite a bit of research on American history. Despite what we were told in elementary school, the Contiinental Congress enaged in negotiations to settle with England. Americans active in the cause believed that George III was a good monarch. Many, such as Washington and Franklin, were in his service. History could have turned out differently.
I was taught that there was no more vile monarch than George III. England was depicted an an absolute dictatorship. Parliament was never discussed. Most Patriots who were viewed as pro-British were Federalist, who wanted a strong central government. John Adams famously suggested that the President of the United States be addressed as "Your majesty."
Won't Charles as king be the litmus test?