No i dont think bitcoin will totally rule over the world .it will be totally different and its limitations will be more than 21 million .all the government will jointly accept and i am sure that it will not be bitcoins at all.
i think still it need a good time rule over the world. actually bitcoin is not yes so much popular in all over the world, it will take a long time when all the people of the world will starting using bitcoin and they will give priority to bitcoin over fiat currency.