Practicality
All these 20th-century views have something in common: they view it as a theoretical work, not a set of guidelines for good governance. Plato scholars see it as their task to provide the background knowledge that is needed to gain a fair understanding of what was meant by the author of the Republic. Then the uniqueness of the Republic shows up in the way it clarifies genuine connections of political causes and effects in real life, precisely by providing them with a heuristically rich context.
Nonetheless Bertrand Russell argues that at least in intent, and all in all not so far from what was possible in ancient Greek city-states, the form of government portrayed in the Republic was meant as a practical one by Plato.
Read more about this topic: Structure Of Plato's Republic, Reception and Interpretation, 20th Century