Given a scholarly definition of "Monarchy" in Political Science or History academia, can you legitimately call the Supreme Leader-led North Korea a "monarchy"?
Given a scholarly definition of "Monarchy"...
As best as I can tell, there is no single definition of a monarchy.
A form of government in which law-making power is given to a single person, usually holding such authority by birthright and not by merit.
Monarchy is a form of rule in which there is a single head of state, a monarch, with the title of King, Queen or similar titleholder. The head of state usually inherits the title through rules of descendency as a member of a specific royal family and holds his or her office for life. The monarch is often believed to have a religious or similar symbolic significance for the state and its institutions that legitimate his or her privileges.
Oxford Dictionaries (UK):
Monarchy: A form of government with a monarch at the head.
Monarch: A sovereign head of state, especially a king, queen, or emperor.
According to the etymology of the word, monarchy is that government in which one person rules supreme—alone. In modern times the terms autocracy, autocrat, have come into use to indicate that monarchy of which the ruler desires to be exclusively considered the source of all power and authority. The Russian emperor styles himself Autocrat of all the Russias. Autocrat is the same with despot ; but the latter term has fallen somewhat into disrepute. Monarchy is contradistinguished from republic. Although the etymology of the term monarchy is simple and clear, it is by no means easy to give a deﬁnition either of monarchy or of republic. ... The fact that one man stands at the head of a government does not make it a monarchy. We have a president at the head. Nor is it necessary that the one person have an unlimited amount of power, to make a government a monarchy. The power of the king of England is limited by law and theory, and reduced to a small amount in reality: yet England is called a monarchy. Nor does hereditariness furnish us with a distinction. The pope is elected by the cardinals, yet the States of the Church were a monarchy ; and the stadtholder of several states of the Netherlands was hereditary, yet the states were republics. We cannot ﬁnd any better definition of monarchy than this : a monarchy is that government which is ruled (really or theoretically) by one man, who is wholly set apart from all other members of the state (called his subjects)
Everyone agrees there's one head of state, and that's about it. There's usually the titles and trappings of kingship, but not always. There's usually hereditary rule, but not always. There might be other sources of power, but the monarch is usually the source of that power.
It's easy to contrast that to a republic/democracy, where the ruler is expressly just another citizen, but contrasting it to other forms of autocracy is much harder.
The Wikipedia page on Family dictatorships has an entirely unsourced definition which I rather like:
In [an absolute monarchy], the transition of power within a family is required by general law, and continues to apply to all successions in the regime. In [a family dictatorship], this arrangement is not required by general law. In some cases, a special law might be enacted to formally nominate one particular family member of the present leader as the successor. In other cases, the law of the state may even formally provide for elections, but control exerted by the leader on the political and electoral process ensures a hereditary succession. Furthermore, whether each succession succeeds depends on the level of authority and control of the leader.
In other words, the difference between a family dictatorship and an absolute hereditary monarchy is whether or not a rule of succession exists. I think this particular definition satisfies all the scholarly definitions above, including the issues that Bouvier wrestled with. In all his examples of monarchies, there was an explicit method for power to transfer to the new ruler. That doesn't mean the method always worked, but it existed. In contrast, a dictatorship (family or otherwise) relies on each leader to explicitly choose their successor, and has no mechanism for replacing a leader who died before making that choice.
... can you call North Korea a "monarchy"?
Given that there is no single definition, you can certainly try. North Korea certainly meets Oxford's definition, although not the typical examples given. It matches Duhaime.org's definition, depending on how you read the word "given", and again without matching the "usually". It can match the USLegal definition, if you really stretch it: Supreme Leader as "similar titleholder", ignore the "usually", and if you define socialism as equivalent to a religion, then its leader could be said to hold "similar symbolic significance".
However, I don't think it's possible to stretch Bouvier's definition to fit. While all power ultimately flows from the current leader, they take titles and positions which in theory anyone could fill: Chairman, Secretary, President... All the power comes not from the positions themselves, but what those positions allow them to direct the associated organization to do. (i.e. Chairman has the committee vote to do _______). Whether the specific forms of this are followed, I don't know enough to say, but they at least theoretically exist.
Finally, the "family dictatorship" definition fits much better than that of a monarchy. If Kim Jong-un had a heart attack tomorrow, there is no indiciation as to who his heir would be. In a hereditary monarchy, it could be his daughter (with a regent), or another male descendent of his father. But because he hasn't named anyone, there is no continuity of government.