I think the problem would be how can you realisticaly have a religion based government for the short term. I'm no Islam expert but I think the rules are supposed to be static for the long haul.

Also a religious government might make life very uncomfertable for secular people. More uncomfortable then say, a Republican controlled government for Democrats was. Even if more than half wanted it, if it was only a slim margin would it be fair to force all the laws of Islam on non believers all at once (this is a very unlikely scenario i realize)?