As long as we have nation-states, including the United Kingdom, I see little reason to do away with such an integral part of ours as the monarchy, and even if we do as a species manage to move beyond the concept some day as we continue to better ourselves I would hope that we would have the technology available to create a true, direct democracy through the internet (or a successor to it) or a neural network or some such thing rather than invest our hopes for democracy in a bunch of corrupt plutocratic demagogues as republics have done in the present day. Essentially, I see modern constitutional monarchies and republics as about the same in terms of democratic credentials, and there's no point changing from one to the other against our traditions until something radically better comes along.