Biggest threat to Bitcoin, globally, is certainly the way people react to new things. Many of the great technological breakthroughs were diminished through history. People are afraid of the unknown. Bitcoin is on a good way to overcome this issue, since the entire market of cryptocurrencies is getting more and more adopted globally. People are beginning to see Bitcoin as a valid method of payment with many benefits.
Still, there are some unresolved issues, especially considering some of the aspects of the Bitcoin network itself. That can put in danger entire network, but Bitcoin showed through years to have a great ability to overcome all the issues and evolve into something bigger.
It is pretty much the same with every new concept. It is most important that society accepts it as something substantial and safe. Bitcoin came a long way, but still there are plenty of people which will hardly accept this sort of libertarian concept. Innovators, early adopters are an easy task for every good concept but Bitcoin is now at the crossroads, since the bigger and more conservative part of the global society is yet to approve this idea. Nevertheless, Bitcoin came a long way and it is on a good way to become present in everyday life. Already now you can buy almost anything with Bitcoin online, and in many physical stores as well.
With the expansion of Bitcoin globally, altruistic concept of Bitcoin mining that will allow anyone with a solid mining rig to earn through enabling Bitcoin peer-to-peer transaction is almost over. Today, with classical mining there is little to none of the incentive that miners used to receive. It is hard to believe that Bitcoin is going to maintain its decentralization once the need for hardware outgrows even the modern cloud mining. Centralization of Bitcoin seems to be inevitable future, but there are many people who are trying to figure out solution of this problem. Seems that today, confirmations of Bitcoin transactions will be able to achieve only those with expensive ASIC components.
Many of the countries worldwide are investigating Bitcoin and there is a reasonable presumption that many of them will once consider Bitcoin illegal. That type of overreacting creates an unwelcoming climate for cryptocurrencies, since the adoption is a key element in the evolution of Bitcoin.
In China, government is ceasing many Bitcoin operators and it seems that in recent future it will become illegal activity to trade on the market of cryptocurrencies. Also, there have been many actions against Bitcoiners in India, where Bitcoin is already seen as a threat to traditional value system. Still, with decentralized concept of Bitcoin it is hard to imagine complete ban of Bitcoin transactions since they see no borders. It is obvious that elite parts of the global society see the threat in Bitcoin since it is open for everyone and there are no chances for control.