What do you think can be the biggest threat for Bitcoin in current situation? In my opinion it can be only some sudden governments shift in regulations and laws to ban Bitcoin (which I don't really think may happen), otherwise there are basically no obstacles or threats.
Government prohibitions, market shift, and new innovations in cryptocurrencies.
Those are some of the factors that may render BTC obsolete in the following years to come. But government prohibitions might be one of the biggest cause that may cause BTC to fall in its price. Imagine if countries were to prohibit the regulation and transaction of such coins. From that perspective alone, millions of people/users would face such inconvenience in which BTC is trying to provide.