Per http://www.huffingtonpost.com/david-n-myers/kiryas-yoel-theocracy-in-america_b_1124505.html - "...Judge Rakoff upheld the legal validity of Kiryas Joel, New York. In doing so, he rejected the proposition that the Village constitutes an impermissible "theocracy," and affirmed, perhaps unintentionally, another well-established American tradition: the granting of government sanction to strong forms of religious sub-communities, even (or perhaps especially) those whose norms of governance and behavior are illiberal and seemingly in contradiction to American constitutional values and norms...American courts have repeatedly approved the formation of private self-governing enclaves by religiously homogeneous communities. Kiryas Joel thus falls into a long American tradition of robust support for religious sub-communities, a tradition that enables private communities to form and then, once formed, to translate their private power into political power..."
So it is legally permissible to establish a theocratic community in the USA. It is important to establish a reformed Christian theocratic community in the USA because we need to provide an example of how God prospers a reformed Christian theocracy as way of convincing more people to embrace the idea. More importantly, a reformed Christian theocracy brings glory to God.