The number 1 problem with any attempt at creating a currency is adoption. Efficiency is irrelevant in the face of this fact. The problem with bitcoin is the promise of adoption right around the corner. There are many reasons why Bitcoin is unlikely to become mainstream, and perhaps the most important is the absence of poor people in the bitcoin community.
It is easier to get poor people to buy diamonds than it is to get them to invest in bitcoin. Worse still, it is easier to get poor people to invest in bitconnect than to buy bitcoin. If you know anything about network value, you know it starts with aggressive marketing. The more people you convince to buy your idea, the more valuable it becomes and the more people are convinced its a good investment.
So what happened with bitcoin at the end of 2017? Bitcoin popularity exploded along with its price. Which came first, the price increase or the popularity? I think it's a feedback loop that has many factors. These factors include the rise of lending/investing programs with their aggressive campaigns, the drama resulting from the forks, the explosion of ERC tokens with aggressive campaigns, bitcoin futures launch and the price surge. Unfortunately, many of these factors are also the reason why bitcoin will probably fade into obscurity.
If bitcoin was going to become mainstream, that was the time for mass adoption. In fact, it looked like that was beginning to happen until all the problems associated with factors that popularized bitcoin began surfacing. Many investing/lending programs started closing down in what seemed like fall of Ponzi schemes. While the forks created drama that created chatter about bitcoin, they ultimately created more confusion for the newcomers. Some people lost money by confusing bitcoin cash and bitcoin. Some others lost money by trying to redeem new forked tokens. Many ERC tokens were simply money grabs with no real utility. Some of the tokens were simply pumped then dumped on unsuspecting buyers (ripple). The futures launch was supposed to mean wall street money coming into crypto, but in reality, it achieved the opposite effect. The wall street money could stay outside of cryptos by creating a derivative market where they could receive all the gains without actually investing in the actual technology. It also created another entity for people to be worried about in terms of price manipulation. The price surge ultimately created a bull trap for those who came in hoping for riches only to find themselves at a loss when the price more than halved its peak value.
In addition to those problems, other problems surfaced that just showed the infancy of bitcoin. During the price surge, one of the selling points was the ability to use bitcoin as currency because it was already accepted as such on many platforms. Unfortunately, many of those platforms had to suspend bitcoin transactions due to transaction fees becoming too high. Many newcomers also discovered just how difficult it is to use bitcoin (sending and receiving from wallets). Then there were concerns about how the government was going to treat bitcoin. The average Joe who decided to try out bitcoin could not have had a very positive experience. Those who didn't invest were vindicated.
Where does all this leave bitcoin? The holders (hodlers) of bitcoin are now developers, traders, miners and early/wealthy investors. The popularity did not lead to increased value for bitcoin. My intuition is that bitcoin has missed its moment. Ideally, what you want in a brand is for popularity to propel you into mainstream acceptance. Once you miss that boat, nothing short of a brilliant advertising campaign can rescue you from insignificance (see bitconnect for marketing done right).
Another major impediment to adoption is the current state of our economy. The fact that so many Americans live paycheck to paycheck means very little is left for saving. In that sense, bitcoin is like stock investing, only the eccentric or wealthy can afford it. This means satoshi's dream of creating a currency for helping people escape government financial policies is least likely to help the very people it was created for. The majority of investors in bitcoin have other means of protecting themselves from government fiscal policies (see investing in gold).
The last hope bitcoin had as a black market currency is currently being challenged by other cryptos more suited to the task (see monero). No matter what optimistic lens you put on, things are looking dire for bitcoin. Instead of seeing this as a death knell for bitcoin, I see it as an opportunity for someone to come along and create the crypto we've all been waiting for (definitely not nano).