An Islamic Republic with the proper respect for human rights, can in time become more secular, or less Islamicist. The economic benefits of freedom and liberty engender and strengthen that freedom and liberty.
Once we're past the danger point of Iraq and Afghanistan succumbing to Sharia Law, the primary worry we'll have will be about them swinging in the opposite direct toward European style hedonism and socialism. Both extremes encourage and promote disenfranchisement and big government, though the socialist extreme is considerably more subtle than the theocracy.
Again, that sounds great. But it all depends on the creep of Islam. Islam is a cancer on any society it touches. If Europe is at risk of becoming part of the caliphate, how much more at risk is a country where nearly everyone is muslim.