While the traditional view of Plato's Republic is that it is a political treatise discussing the best form of government, allegedly inspired by the disciplined, austere, oligarchic Spartan example as opposed to the decadent, undisciplined, democratic Athenian example, the Robin Waterfield edition of the work offers a different angle, to wit, that Plato's Republic is a psychological treatise recommending the rule of reason over the passions.
Thus, the philosopher-kings are none other than the two sides of the neocortex, which enable higher brain functions, including reason, and that the lower you go in the ideal community, the baser the brain function, with the reptilian, basic survival mechanism at the bottom.
The community as portrayed by Plato in his book is really an allegory for healthy psychology, where consciousness is unified and not led astray by emotionality taking over or basic instincts such as lust and survival counting for more than their fair share.
It seems to me that the work operates on both levels, i.e. a psychological internal level and a political external level, understanding as the mysteries-initiate Plato did that it takes knowing oneself and mastering one's inner kingdom to get a grip on the reality outside and the external kingdom of human society.
Nonetheless it could be convincingly and respectably argued that a community where all are masters of themselves, unified and internally harmonious, has no need for 'philosopher-kings' because where all are internal monarchs, external anarchy manifests, i.e. where one and all is his or her own master, there is no room for capriciously designated leaders to rule others from on high with the effect of enslaving the latter.