Indeed this does not break any rules and it is allowed. Not many players use it because even though it gives you an early advantage in science it dampens your early growth which will negatively affect you later on. Xin's strategy is good for very inhospitable terrain where good city sites are hard to find and specials are grass covered or unsuitable for early game (Iron, coal, oil, ...) but I doubt if it gives you any advantage in good terrain where your early workers are all working specials.
