If you look at Bitcoin's current model, it's decentralized. This means that it's impossible to become the reserve currency of the world in its current state, as no one can control its supply or issue the same. For Bitcoin to achieve its status as a reserve currency, it would need to become centralized without a doubt. Only that way, governments could easily manipulate it by either issuing more coins (inflation) or restrict access to the same. Like I said before, I once thought that Bitcoin could become a reserve currency of the world because it was growing in popularity.
However, upon realizing that most governments have been against decentralization, it's hard to believe that Bitcoin will become the reserve currency of the world anytime soon. Despite this, the US Dollar might continue to be the world's reserve currency for quite some time. Even if the US Dollar gets displaced in the future, cryptocurrencies like Bitcoin won't get chance of becoming the world's reserve currency. Instead, another centralized Fiat currency issued by the government will take the lead in case the USD fails. It could be the Euro, the GBP, the Yen, or even the Chinese Yuan.